Exhibit 5.1

Michael E. Tenta

T: +1 650 843 5636

mtenta@cooley.com

March 31, 2014

Versartis, Inc.

275 Shoreline Drive, Suite 450

Redwood City, CA 94065

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection with the filing by Versartis, Inc., a Delaware corporation (the “Company”), of a Registration Statement on Form S 8 (the “Registration Statement”) with the Securities and Exchange Commission covering the offering of up to an aggregate of 6,184,337 of the Company’s Common Stock, par value $0.0001 per share, including (a) 1,934,082 shares of Common Stock (the “2009 Shares”) pursuant to the Company’s 2009 Stock Plan, as amended (the “2009 Plan”), (b) 4,100,255 shares of Common Stock (the “2014 Shares”) pursuant to the Company’s 2014 Equity Incentive Plan (the “2014 Plan”), and (c) 150,000 shares of Common Stock (the “2014 ESPP Shares”) pursuant to the Company’s 2014 Employee Stock Purchase Plan (the “2014 ESPP” and together with the 2009 Plan and the 2014 Plan, the “Plans”).

In connection with this opinion, we have examined and relied upon (a) the Registration Statement and related prospectuses, (b) the Plans, (c) the Company’s Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws, each as currently in effect, and (d) such other documents, records, certificates, memoranda and other instruments as in our judgment are 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, the conformity to originals of all documents submitted to us as copies thereof, and the due execution and delivery of all documents where due execution and delivery are a prerequisite to the effectiveness thereof.

As to certain factual matters, we have relied upon a certificate of an officer of the Company and have not sought to verify independently such matters. Our opinion is expressed only with respect to the General Corporation Law of the State of Delaware.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the 2009 Shares, the 2014 Shares and the 2014 ESPP Shares, when sold and issued in accordance with the 2009 Plan, the 2014 Plan and the 2014 ESPP, respectively, and the Registration Statement and related prospectuses, will be validly issued, fully paid, and nonassessable (except as to shares issued pursuant to certain deferred payment arrangements, which will be fully paid and nonassessable when such deferred payments are made in full).

FIVE PALO ALTO SQUARE, 3000 EL CAMINO REAL, PALO ALTO, CA 94306-2155 T: (650) 843-5000 F: (650) 849-7400 WWW.COOLEY.COM

Versartis, Inc.

Page Two

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

Sincerely,

Cooley LLP
By:	/s/ Michael E. Tenta
	Michael E. Tenta

FIVE PALO ALTO SQUARE, 3000 EL CAMINO REAL, PALO ALTO, CA 94306-2155 T: (650) 843-5000 F: (650) 849-7400 WWW.COOLEY.COM