UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                  SCHEDULE 13G

                    Under the Securities Exchange Act of 1934
                                (Amendment No. )*

                          Momenta Pharmaceuticals, Inc.
--------------------------------------------------------------------------------
                                (Name of Issuer)

                    Common Stock, $.0001 Par Value Per Share
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    60877T101
                                    ---------
                                 (CUSIP Number)

                                  June 16, 2005
                                  -------------
                      (Date of Event which Requires Filing
                               of this Statement)


Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

                                [ ] Rule 13d-1(b)
                                [X] Rule 13d-1(c)
                                [ ] Rule 13d-1(d)


*The  remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for any  subsequent  amendment  containing  information  which  would  alter the
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act") or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).





<PAGE>


--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  2  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           S.A.C. Capital Advisors, LLC
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              3,900 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            3,900 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           3,900 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           Less than 0.1% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 2 of 13


<PAGE>


--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  3  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           S.A.C. Capital Management, LLC
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              3,900 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            3,900 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           3,900 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           Less than 0.1% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 3 of 13


<PAGE>



--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  4  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           S.A.C. MultiQuant Fund, LLC
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           Anguilla, British West Indies
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              3,900 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            3,900 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           3,900 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           Less than 0.1% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 4 of 13




<PAGE>

--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  5  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Sigma Capital Management, LLC
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           Delaware
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              2,108,210 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            2,108,210 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           2,108,210 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           8.3% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 5 of 13


<PAGE>

--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  6  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Sigma Capital Associates, LLC
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           Anguilla, British West Indies
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              2,108,210 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            2,108,210 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           2,108,210 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           8.3% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           00
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 6 of 13


<PAGE>

--------------------------------------          --------------------------------
CUSIP No. 60877T101                      13G      Page  7  of 13 Pages
--------------------------------------          --------------------------------

---------- ---------------------------------------------------------------------
        1  NAME OF REPORTING PERSON
           I.R.S. IDENTIFICATION NO. OF ABOVE PERSON

           Steven A. Cohen
---------- ---------------------------------------------------------------------
        2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
                                                                     (a) [ ]
                                                                     (b) [X]

---------- ---------------------------------------------------------------------
        3  SEC USE ONLY
---------- ---------------------------------------------------------------------
        4  CITIZENSHIP OR PLACE OF ORGANIZATION

           United States
--------------------- ----- ----------------------------------------------------
                         5  SOLE VOTING POWER

                            0

      NUMBER OF       ----- ----------------------------------------------------
        SHARES           6  SHARED VOTING POWER
   BENEFICIALLY OWNED  
       BY EACH              2,112,110 (see Item 4)
   REPORTING PERSON   ----- ----------------------------------------------------
        WITH             7  SOLE DISPOSITIVE POWER

                            0
                      ----- ----------------------------------------------------
                         8  SHARED DISPOSITIVE POWER

                            2,112,110 (see Item 4)
---------- ---------------------------------------------------------------------
        9  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

           2,112,110 (see Item 4)
---------- ---------------------------------------------------------------------
       10  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES

            [ ]

---------- ---------------------------------------------------------------------
       11  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

           8.3% (see Item 4)
---------- ---------------------------------------------------------------------
       12  TYPE OF REPORTING PERSON*

           IN
---------- ---------------------------------------------------------------------
                       *SEE INSTRUCTION BEFORE FILLING OUT

                                  Page 7 of 13


<PAGE>


Item 1(a)           Name of Issuer:
                    --------------

                    Momenta Pharmaceuticals, Inc.

Item 1(b)           Address of Issuer's Principal Executive Offices:
                    -----------------------------------------------

                    675 West Kendall Street
                    Cambridge, MA 02142

Items 2(a)          Name of Person Filing:
                    ----------------------

                    This  statement  is filed by: (i) S.A.C.  Capital  Advisors,
                    LLC,  ("SAC  Capital  Advisors")  with  respect to shares of
                    common stock,  $0.0001 par value per share ("Shares") of the
                    Issuer beneficially owned by and S.A.C. MultiQuant Fund, LLC
                    ("SAC MultiQuant");  (ii) S.A.C.  Capital  Management,  LLC,
                    ("SAC   Capital   Management")   with   respect   to  Shares
                    beneficially  owned by SAC MultiQuant;  (iii) SAC MultiQuant
                    with respect to Shares  beneficially owned by it; (iv) Sigma
                    Capital  Management,  LLC ("Sigma Capital  Management") with
                    respect  to  Shares  beneficially  owned  by  Sigma  Capital
                    Associates,  LLC  ("Sigma  Capital  Associates");  (v) Sigma
                    Capital Associates with respect to Shares beneficially owned
                    by it;  and (vi)  Steven A.  Cohen  with  respect  to Shares
                    beneficially  owned by SAC  Capital  Advisors,  SAC  Capital
                    Management,  SAC  MultiQuant,  Sigma Capital  Management and
                    Sigma Capital Associates.

Item 2(b)           Address of Principal Business Office:
                    -------------------------------------

                    The  address  of the  principal  business  office of (i) SAC
                    Capital  Advisors and Mr.  Cohen is 72 Cummings  Point Road,
                    Stamford, Connecticut 06902, (ii) SAC Capital Management and
                    Sigma Capital  Management is 540 Madison  Avenue,  New York,
                    New York 10022,  and (iii) SAC  MultiQuant and Sigma Capital
                    Associates  is P.O.  Box 58,  Victoria  House,  The  Valley,
                    Anguilla, British West Indies.

Item 2(c)           Citizenship:
                    ------------

                    SAC  Capital  Advisors,  SAC  Capital  Management  and Sigma
                    Capital Management are Delaware limited liability companies.
                    SAC  MultiQuant  and Sigma Capital  Associates are Anguillan
                    limited  liability  companies.  Mr. Cohen is a United States
                    citizen.

Item 2(d)           Title of Class of Securities:
                    -----------------------------

                    Common Stock, par value $.0001 per share

                                  Page 8 of 13

<PAGE>

Item 2(e)           CUSIP Number:
                    -------------

                    60877T101

Item 3              Not Applicable

Item 4              Ownership:
                    ----------

                    The  percentages  used herein are calculated  based upon the
                    Shares issued and  outstanding as of May 5, 2005 as reported
                    on the  Issuers's  quarterly  report on Form 10-Q filed with
                    the  Securities  and Exchange  Commission by the Company for
                    the quarter ended March 31, 2005.

                    As of the close of business on June 24,
2005:

                    1. S.A.C. Capital Advisors, LLC
                    (a) Amount beneficially owned: 3,900
                    (b) Percent of class: Less than 0.1%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 3,900
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         3,900

                    2. S.A.C. Capital Management, LLC
                    (a) Amount beneficially owned: 3,900
                    (b) Percent of class: Less than 0.1%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 3,900
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         3,900


                    3. S.A.C. MultiQuant Fund, LLC
                    (a) Amount beneficially owned: 3,900
                    (b) Percent of class: Less than 0.1%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 3,900
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         3,900

                                  Page 9 of 13

<PAGE>


                    4. Sigma Capital Management, LLC
                    (a) Amount beneficially owned: 2,108,210
                    (b) Percent of class: 8.3%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 2,108,210
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         2,108,210

                    5. Sigma Capital Associates LLC
                    (a) Amount beneficially owned: 2,108,210
                    (b) Percent of class: 8.3%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 2,108,210
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         2,108,210

                    6. Steven A. Cohen
                    (a) Amount beneficially owned: 2,112,110
                    (b) Percent of class: 8.3%
                    (c)(i) Sole power to vote or direct the vote: -0-
                    (ii) Shared power to vote or direct the vote: 2,112,110
                    (iii) Sole power to dispose or direct the disposition: -0-
                    (iv) Shared power to dispose or direct the disposition:
                         2,112,110

                    SAC Capital Advisors, SAC Capital Management,  Sigma Capital
                    Management,  and Mr. Cohen own directly no Shares.  Pursuant
                    to investment  agreements,  each of SAC Capital Advisors and
                    SAC Capital Management share all investment and voting power
                    with  respect  to the  securities  held  by SAC  MultiQuant.
                    Pursuant  to  an  investment  management  agreement,   Sigma
                    Capital  Management  maintains  investment  and voting power
                    with  respect  to  the  securities  held  by  Sigma  Capital
                    Associates. Mr. Cohen controls each of SAC Capital Advisors,
                    SAC Capital  Management  and Sigma  Capital  Management.  By
                    reason of the  provisions  of Rule  13d-3 of the  Securities
                    Exchange  Act of 1934,  as amended,  each of (i) SAC Capital
                    Advisors, SAC Capital Management and Mr. Cohen may be deemed
                    to own beneficially 3,900 Shares (constituting approximately
                    less than 0.1% of the  Shares  outstanding)  and (ii)  Sigma
                    Capital  Management  and  Mr.  Cohen  may be  deemed  to own
                    beneficially  2,108,210 Shares  (constituting  approximately
                    8.3%  of  the  Shares  outstanding).  Each  of  SAC  Capital
                    Advisors,  SAC Capital Management,  Sigma Capital Management
                    and Mr. Cohen  disclaim  beneficial  ownership of any of the
                    securities covered by this statement.

                                 Page 10 of 13


<PAGE>


Item 5              Ownership of Five Percent or Less of a Class:
                    -------------------------------------------- 

                    If this  statement is being filed to report the fact that as
                    of the date hereof the reporting person has ceased to be the
                    beneficial  owner of more than five  percent of the class of
                    securities, check the following.

Item 6              Ownership of More than Five Percent on Behalf of Another
                    --------------------------------------------------------
                    Person:
                    -------

                    Not Applicable

Item 7              Identification and Classification of the
                    ----------------------------------------
                    Subsidiary Which Acquired the Security Being
                    --------------------------------------------
                    Reported on By the Parent Holding Company:
                    ----------------------------------------- 

                    Not Applicable

Item 8              Identification and Classification of Members 
                    ---------------------------------------------
                    of the Group:
                    ------------ 

                    Not Applicable

Item 9              Notice of Dissolution of Group:
                    ------------------------------ 

                    Not Applicable

Item 10             Certification:
                    --------------

         By signing below the signatory certifies that, to the best of his
knowledge and belief, the securities referred to above were not acquired and are
not held for the purpose of or with the effect of changing or influencing the
control of the issuer of the securities and were not acquired and are not held
in connection with or as a participant in any transaction having that purpose or
effect.

                                 Page 11 of 13


<PAGE>


                                    SIGNATURE
                                    ---------

     After  reasonable  inquiry and to the best of my  knowledge  and belief,  I
certify that the information  set forth in this statement is true,  complete and
correct.


Dated:  June 27, 2005


S.A.C. CAPITAL ADVISORS, LLC


By: /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person


S.A.C. CAPITAL MANAGEMENT, LLC


By:  /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person


S.A.C. MULTIQUANT FUND, LLC


By:  /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person


SIGMA CAPITAL MANAGEMENT, LLC


By:  /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person

                                 Page 12 of 13


<PAGE>



SIGMA CAPITAL ASSOCIATES, LLC


By:  /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person


STEVEN A. COHEN


By:  /s/ Peter Nussbaum
   -----------------------------------------
Name:   Peter Nussbaum
Title:  Authorized Person


                                 Page 13 of 13