Post-effective Amendment (investment Company, Rule 485(b)) (485bpos)

Securities Act of 1933 Registration No. 333-186372

Investment Company Act of 1940 Registration No. 811-22796

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 [X]

[ ] Pre-Effective Amendment No.  ______

[X] Post-Effective Amendment No.  14

and

REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940 [X]

[X] Amendment No.  14

Fidelity Merrimack Street Trust

 (Exact Name of Registrant as Specified in Charter)

245 Summer Street, Boston, Massachusetts 02210

(Address of Principal Executive Offices)(Zip Code)

Registrant’s Telephone Number: 617-563-7000

Cynthia Lo Bessette, Secretary

245 Summer Street

Boston, Massachusetts 02210

(Name and Address of Agent for Service)

It is proposed that this filing will become effective immediately upon filing pursuant to paragraph (b) of Rule 485.

EXHIBIT INDEX

Exhibit	Exhibit No.
XBRL Instance Document	EX-101.INS
XBRL Taxonomy Extension Schema Document	EX-101.SCH
XBRL Taxonomy Extension Calculation Linkbase Document	EX-101.CAL
XBRL Taxonomy Extension Definition Linkbase Document	EX-101.DEF
XBRL Taxonomy Extension Labels Linkbase Document	EX-101.LAB
XBRL Taxonomy Extension Presentation Linkbase Document	EX-101.PRE

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for the effectiveness of this Registration Statement pursuant to Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No. 14 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Boston, and Commonwealth of Massachusetts, on the 15th day of January 2020.

	Fidelity Merrimack Street Trust
	By	/s/Laura M. Del Prato
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||		Laura M. Del Prato, President

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

(Signature)		(Title)	(Date)
/s/Laura M. Del Prato		President and Treasurer	January 15, 2020
Laura M. Del Prato		(Principal Executive Officer)
/s/ John J. Burke III		Chief Financial Officer	January 15, 2020
John J. Burke III		(Principal Financial Officer)
/s/Abigail P. Johnson	†	Trustee	January 15, 2020
Abigail P. Johnson
/s/Elizabeth S. Acton	*	Trustee	January 15, 2020
Elizabeth S. Acton
/s/Ann E. Dunwoody	*	Trustee	January 15, 2020
Ann E. Dunwoody
/s/John Engler	*	Trustee	January 15, 2020
John Engler
/s/Robert F. Gartland	*	Trustee	January 15, 2020
Robert F. Gartland
/s/Arthur E. Johnson	*	Trustee	January 15, 2020
Arthur E. Johnson
/s/Michael E. Kenneally	*	Trustee	January 15, 2020
Michael E. Kenneally
/s/Marie L. Knowles	*	Trustee	January 15, 2020
Marie L. Knowles
/s/Mark A. Murray	*	Trustee	January 15, 2020
Mark A. Murray
/s/Jennifer Toolin McAuliffe	*	Trustee	January 15, 2020
Jennifer Toolin McAuliffe

†	By:	/s/ Kevin M. Meagher
		Kevin M. Meagher, pursuant to a power of attorney dated September 30, 2018 and filed herewith.
*	By:	/s/Megan C. Johnson
		Megan C. Johnson, pursuant to a power of attorney dated January 1, 2019 and filed herewith.

POWER OF ATTORNEY

We, the undersigned Directors or Trustees, as the case may be, of the following investment companies:

Fidelity Aberdeen Street Trust Fidelity Advisor Series II Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Colchester Street Trust Fidelity Court Street Trust Fidelity Court Street Trust II Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust Fidelity Merrimack Street Trust

Fidelity Money Market Trust Fidelity Municipal Trust Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Oxford Street Trust II Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned individuals serve as Directors or Trustees (collectively, the “Funds”), hereby revoke all previous powers of attorney we have given to sign and otherwise act in our names and behalf in matters involving any investment company for which FMR or an affiliate acts as investment adviser and hereby constitute and appoint Thomas C. Bogle, John V. O’Hanlon, Robert W. Helm, Megan C. Johnson, and Anthony H. Zacharski, each of them singly, our true and lawful attorneys-in-fact, with full power of substitution, and with full power to each of them, to sign for us and in our names in the appropriate capacities, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in our names and behalf in connection therewith as said attorneys-in-fact deem necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  We hereby ratify and confirm all that said attorneys-in-fact or their substitutes may do or cause to be done by virtue hereof.  This power of attorney is effective for all documents filed on or after January 1, 2019.

WITNESS our hands on this first day of January 2019.

/s/Elizabeth S. Acton	/s/Michael E. Kenneally
Elizabeth S. Acton	Michael E. Kenneally
/s/Ann E. Dunwoody	/s/Marie L. Knowles
Ann E. Dunwoody	Marie L. Knowles
/s/John Engler	/s/Jennifer Toolin McAuliffe
John Engler	Jennifer Toolin McAuliffe
/s/Robert F. Gartland	/s/Mark A. Murray
Robert F. Gartland	Mark A. Murray
/s/Arthur E. Johnson
Arthur E. Johnson

POWER OF ATTORNEY

I, the undersigned Trustee of the following investment companies:

Fidelity Aberdeen Street Trust Fidelity Advisor Series II Fidelity Advisor Series IV Fidelity Boylston Street Trust Fidelity California Municipal Trust Fidelity California Municipal Trust II Fidelity Central Investment Portfolios II LLC Fidelity Charles Street Trust Fidelity Colchester Street Trust Fidelity Court Street Trust Fidelity Court Street Trust II Fidelity Garrison Street Trust Fidelity Hereford Street Trust Fidelity Income Fund Fidelity Massachusetts Municipal Trust

Fidelity Merrimack Street Trust Fidelity Money Market Trust Fidelity Municipal Trust Fidelity Municipal Trust II Fidelity Newbury Street Trust Fidelity New York Municipal Trust Fidelity New York Municipal Trust II Fidelity Oxford Street Trust Fidelity Oxford Street Trust II Fidelity Phillips Street Trust Fidelity Revere Street Trust Fidelity Salem Street Trust Fidelity School Street Trust Fidelity Union Street Trust Fidelity Union Street Trust II Variable Insurance Products Fund V

in addition to any other Fidelity Fund for which the undersigned individual serves as Trustee (collectively, the “Funds”), hereby constitute and appoint Kevin M. Meagher, my true and lawful attorney-in-fact, with full power of substitution, and with full power to sign for me and in my name in the appropriate capacity, all Registration Statements of the Funds on Form N-1A, or any successors thereto, any and all subsequent Amendments, Pre-Effective Amendments, or Post-Effective Amendments to said Registration Statements or any successors thereto, and any supplements or other instruments in connection therewith, and generally to do all such things in my name and behalf in connection therewith as said attorney-in-fact deems necessary or appropriate, to comply with the provisions of the Securities Act of 1933 and the Investment Company Act of 1940, and all related requirements of the Securities and Exchange Commission.  I hereby ratify and confirm all that said attorney-in-fact or his substitutes may do or cause to be done by virtue hereof.  

This Power of Attorney shall remain in full force and effect only for such time as Kevin M. Meagher shall continue to be an officer of Fidelity Management & Research Company, provided that, notwithstanding the foregoing, this Power of Attorney may be revoked at any time by the undersigned in writing.

This Power of Attorney has been executed as of September 30, 2018.

/s/Abigail P. Johnson
Abigail P. Johnson