UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 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): May 19, 2015

Momenta Pharmaceuticals, Inc.

(Exact name of registrant as specified in its 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):

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

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

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

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

Item 8.01.                                        Other Events.

On May 19, 2015, Momenta Pharmaceuticals, Inc. (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman, Sachs & Co. and J.P. Morgan Securities LLC, as representatives of the several underwriters named therein (the “Underwriters”), in connection with the public offering, issuance and sale by the Company of 7,250,000 shares of the Company’s common stock, par value $0.0001 per share, at the public offering price of $19.00 per share, less underwriting discounts and commissions, pursuant to an effective registration statement on Form S-3 (File No. 333-188227) and a related prospectus supplement filed with the Securities and Exchange Commission.  Under the terms of the Underwriting Agreement, the Company has also granted the Underwriters an option exercisable for 30 days to purchase up to an additional 1,087,500 shares of its common stock at the public offering price, less underwriting discounts and commissions.

The Company expects to receive net proceeds from the offering of approximately $129.2 million, or approximately $148.6 million if the Underwriters exercise their option to purchase additional shares in full, after deducting underwriting discounts and commissions and estimated offering expenses. The Company intends to use the net proceeds of the offering for general corporate purposes, including working capital.

The Underwriting Agreement contains customary representations, warranties and agreements by the Company, customary conditions to closing, indemnification obligations of the Company and the Underwriters, including for liabilities under the Securities Act of 1933, as amended, other obligations of the parties and termination provisions.

The above description of the Underwriting Agreement is qualified in its entirety by reference to the full text of the Underwriting Agreement, a copy of which is filed as Exhibit 1.1 hereto and is incorporated herein by reference.

Latham & Watkins LLP, counsel to the Company, has issued an opinion to the Company, dated May 20, 2015, regarding the validity of the shares of common stock to be issued and sold in the offering.  A copy of the opinion is filed as Exhibit 5.1 to this Current Report on Form 8-K.

Item 9.01                                           Financial Statements and Exhibits.

(d) Exhibits:

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SIGNATURES

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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EXHIBIT INDEX

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