Initial Statement of Beneficial Ownership (3)

FORM 3	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES	OMB APPROVAL OMB Number: 3235-0104 Estimated average burden hours per response... 0.5
	Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

1. Name and Address of Reporting Person * KWON YOUNG	2. Date of Event Requiring Statement (MM/DD/YYYY) 3/7/2018	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 /
(Street) CAMBRIDGE, MA 02142        (City)              (State)              (Zip)	5. If Amendment, Date Original Filed (MM/DD/YYYY)	6. Individual or Joint/Group Filing (Check Applicable Line) _ X _ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person

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	142411	D

Table II - Derivative Securities Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security (Instr. 4)	2. Date Exercisable and Expiration Date (MM/DD/YYYY)		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)	2/22/2021	Common Stock	62000	$13.26	D
Stock Option (Right to Buy)	(2)	2/14/2022	Common Stock	30000	$15.44	D
Stock Option (Right to Buy)	(3)	2/19/2023	Common Stock	30800	$12.58	D
Stock Option (Right to Buy)	(4)	2/18/2024	Common Stock	38575	$17.96	D
Stock Option (Right to Buy)	(5)	2/18/2025	Common Stock	37725	$13.02	D
Stock Option (Right to Buy)	(6)	8/11/2025	Common Stock	20000	$21.56	D
Stock Option (Right to Buy)	(7)	2/9/2026	Common Stock	37800	$10.83	D
Stock Option (Right to Buy)	(8)	2/7/2027	Common Stock	45100	$18.85	D
Restricted Stock Units	(9)	(9)	Common Stock	16913	(10)	D
Restricted Stock Units	(11)	(11)	Common Stock	55000	(10)	D

Explanation of Responses:
(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.

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			SVP, Corporate Development

Signatures
/s/ Marie T. Washburn as attorney in fact		3/12/2018
** Signature of Reporting Person		Date

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
*	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).
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