Exhibit 5.1

Nicole C. Brookshire

+1 617 937 2357

nbrookshire@cooley.com

April 5, 2019

Millendo Therapeutics, Inc.

301 North Main Street, Suite 100

Ann Arbor, Michigan 48104

Re: Registration on Form S-8

Ladies and Gentlemen:

We have acted as counsel to Millendo Therapeutics, Inc., a Delaware corporation (the “Company”), in connection with the filing of a registration statement on Form S-8 (the “Registration Statement”) with the Securities and Exchange Commission covering the offering of up to 2,203,690 shares of the Company’s Common Stock, par value $0.001 per share, including (a) 447,333 shares of Common Stock (the “OvaScience 2012 Shares”) pursuant to the OvaScience 2012 Stock Incentive Plan, as amended (the “OvaScience 2012 Plan”), (b) 1,439,938 shares of Common Stock (the “Millendo 2012 Shares”) pursuant to the Millendo Therapeutics, Inc. 2012 Stock Plan (the “Millendo 2012 Plan”), (c) 159,700 shares of Common Stock issuable under new hire inducement stock option awards granted by the Company on December 7, 2018, January 15, 2019 and January 31, 2019 (the “Inducement Shares”), pursuant to the terms of stock option grant notices and nonstatutory stock option agreements, and (d) 156,719 shares of Common Stock issuable upon the exercise of outstanding warrants (the “Warrant Shares”) (such warrants and agreements, together with the OvaScience 2012 Plan and the Millendo 2012 Plan, the “Plans”).

In connection with this opinion, we have examined and relied upon the Registration Statement and related prospectuses, the Company’s Amended and Restated Certificate of Incorporation and Bylaws, as currently in effect, the Plans and the originals or copies certified to our satisfaction of such other records, documents, certificates, memoranda and other instruments as we deem necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness and authenticity of all documents submitted to us as originals and the conformity to originals of all documents submitted to us as copies thereof. As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not sought independently to verify such matters.

Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware. We express no opinion to the extent that any other laws are applicable to the subject matter hereof and express no opinion and provide no assurance as to compliance with any federal or state securities law, rule or regulation.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the OvaScience 2012 Shares, the Millendo 2012 Shares, the Inducement Shares, and the Warrant Shares, when

Cooley LLP 500 Boylston Street Boston, MA 02116-3736
t: (617) 937-2300 f: (617) 937-2400 cooley.com

April 5, 2019

sold and issued in accordance with their respective Plans, the Registration Statement and related prospectuses, will be validly issued, fully paid, and nonassessable.

We consent to the filing of this opinion as an exhibit to the Registration Statement.

Sincerely,

COOLEY LLP

By:	/s/ Nicole C. Brookshire
	Nicole C. Brookshire

Cooley LLP 500 Boylston Street Boston, MA 02116-3736
t: (617) 937-2300 f: (617) 937-2400 cooley.com