FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0104 Expires: January 31, 2005 Estimated average burden hours per response... 0.5

(Print or Type Responses)

1. Name and Address of Reporting Person *   KWON YOUNG 2. Date of Event Requiring Statement (Month/Day/Year) 03/07/2018 3. Issuer Name and Ticker or Trading Symbol MOMENTA PHARMACEUTICALS INC [MNTA] (Last) (First) (Middle) C/O MOMENTA PHARMACEUTICALS, INC., 675 WEST KENDALL STREET 4. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) SVP, Corporate Development 5. If Amendment, Date Original Filed(Month/Day/Year) (Street) CAMBRIDGE, MA 02142 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Beneficially Owned

1.Title of Security (Instr. 4) 2. Amount of Securities Beneficially Owned (Instr. 4) 3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5) 4. Nature of Indirect Beneficial Ownership (Instr. 5) Common Stock 142,411 D Â

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.			SEC 1473 (7-02)
	Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (Right to Buy)	  (1)	02/22/2021	Common Stock	62,000	$ 13.26	D	Â
Stock Option (Right to Buy)	  (2)	02/14/2022	Common Stock	30,000	$ 15.44	D	Â
Stock Option (Right to Buy)	  (3)	02/19/2023	Common Stock	30,800	$ 12.58	D	Â
Stock Option (Right to Buy)	  (4)	02/18/2024	Common Stock	38,575	$ 17.96	D	Â
Stock Option (Right to Buy)	  (5)	02/18/2025	Common Stock	37,725	$ 13.02	D	Â
Stock Option (Right to Buy)	  (6)	08/11/2025	Common Stock	20,000	$ 21.56	D	Â
Stock Option (Right to Buy)	  (7)	02/09/2026	Common Stock	37,800	$ 10.83	D	Â
Stock Option (Right to Buy)	  (8)	02/07/2027	Common Stock	45,100	$ 18.85	D	Â
Restricted Stock Units	  (9)	  (9)	Common Stock	16,913	$ (10)	D	Â
Restricted Stock Units	  (11)	  (11)	Common Stock	55,000	$ (10)	D	Â

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
KWON YOUNG C/O MOMENTA PHARMACEUTICALS, INC. 675 WEST KENDALL STREET CAMBRIDGE, MA 02142	Â	Â	  SVP, Corporate Development	Â

Signatures

/s/ Marie T. Washburn as attorney in fact		03/12/2018
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 5(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Subject to the officer's continued service with the company, the stock options will vest with respect to 25% of the shares on the first anniversary of February 22, 2011, and the remainder will vest in equal quarterly installments over the subsequent three years.
(2)	Subject to the officer's continued service with the company, the stock options granted on February 14, 2012 will vest in equal quarterly installments over the four year vesting period.
(3)	Subject to the officer's continued service with the company, the stock options granted on February 19, 2013 will vest in equal quarterly installments over the four year vesting period.
(4)	Subject to the officer's continued service with the company, the stock options granted on February 18, 2014 will vest in equal quarterly installments over the four year vesting period.
(5)	Subject to the officer's continued service with the company, the stock options granted on February 18, 2015 will vest in equal quarterly installments over the four year vesting period.
(6)	Subject to the officer's continued service with the company, the stock options will vest with respect to 25% of the shares on the first anniversary of August 11, 2015, and the remainder will vest in equal quarterly installments over the subsequent three years.
(7)	Subject to the officer's continued service with the company, the stock options will vest with respect to 25% of the shares on the first anniversary of February 9, 2016, and the remainder will vest in equal quarterly installments over the subsequent three years.
(8)	Subject to the officer's continued service with the company, the stock options will vest with respect to 25% of the shares on the first anniversary of February 7, 2017, and the remainder will vest in equal quarterly installments over the subsequent three years.
(9)	Subject to the officer's continued service with the company, the restricted stock units will vest with respect to 25% of the shares on the first anniversary of February 7, 2017, and the remainder will vest in equal quarterly installments over the subsequent three years.
(10)	Each Restricted Stock Unit represents a contingent right to receive one share of MNTA common stock.
(11)	Subject to the officer's continued service with the company, the restricted stock units will vest with respect to 50% of the shares on the first anniversary of February 12, 2018, and the remaining 50% will vest on the second anniversary of the grant date.

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, See Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.