Exhibit 5.1

Michael E. Tenta

+1 650 843 5636

mtenta@cooley.com

March 9, 2017

Versartis, Inc.

4200 Bohannon Drive, Suite 250

Menlo Park, California 94025

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 1,867,975 of the Company’s Common Stock, par value $0.0001 per share, including (a) 1,567,975 shares of Common Stock (the “2014 Shares”) pursuant to the Company’s 2014 Equity Incentive Plan (the “2014 Plan”) and (b) 300,000 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 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 by all parties other than the Company 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 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 as to whether the laws of any particular jurisdiction are applicable to the subject matter of this opinion. We are not rendering any opinion as to compliance with any federal or state antifraud law, rule or regulation relating to securities, or to the sale or issuance thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the 2014 Shares and the 2014 ESPP Shares, when sold and issued in accordance with 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).

3175 HANOVER STREET, PALO ALTO, CA 94304-1130  T: (650) 843-5000  F: (650) 849-7400  WWW.COOLEY.COM

Versartis, Inc.

March 9, 2017

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

3175 HANOVER STREET, PALO ALTO, CA 94304-1130  T: (650) 843-5000  F: (650) 849-7400  WWW.COOLEY.COM