UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of report (Date of earliest event reported): January 19, 2011

Momenta Pharmaceuticals, Inc.

(Exact Name of Registrant as Specified in Charter)

(617) 491-9700

(Registrant’s telephone number,
including area code)

Not applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 5.02       Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

(d)

On January 19, 2011, the Board of Directors (the “Board”) of Momenta Pharmaceuticals, Inc. (the “Company”), upon recommendation of the Nominating and Corporate Governance Committee of the Board, appointed Thomas Koestler to serve as a Class III director to hold office until his successor is elected and qualified.  Effective as of March 1, 2011, Mr. Koestler will serve as a member of the Science and Compensation Committees of the Board.

There is no arrangement or understanding between Mr. Koestler and any other person pursuant to which he was selected as a director of the Company. There are no transactions since the beginning of the Company’s last fiscal year, or any currently proposed transaction, in which the Company was or is a participant, the amount involved exceeds $120,000, and in which Mr. Koestler had, or will have, a direct or indirect material interest.

In connection with Mr. Koestler’s appointment and in accordance with the Company’s director compensation program, Mr. Koestler will be granted an option to purchase 30,000 shares of the Company’s common stock at the next regularly-scheduled meeting of the Board, with an exercise price equal to the closing price of the common stock the day before such meeting.  The option will vest quarterly over the three years following the date of grant, subject to Mr. Koestler’s continued service on the Board.  The option will be issued under the Company’s 2004 Stock Incentive Plan, as amended, pursuant to the terms and conditions of the Form of Nonstatutory Stock Option Agreement under such Plan. The Company’s form of Nonstatutory Stock Option Agreement was filed as Exhibit 10.2 to the Company’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2004 and is incorporated herein by reference.  As a non-employee director, Mr. Koestler will be entitled to annual stock option awards and certain retainer fees in accordance with the Company’s director compensation program.  The Company’s Non-Employee Director Compensation Summary was filed as Exhibit 10.25 to the Company’s Annual Report on Form 10-K for the year ended December 31, 2009 and is incorporated herein by reference.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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