Exhibit 5.1

Matthew T. Browne

+1 858 550 6045

mbrowne@cooley.com

August 21, 2015

Regulus Therapeutics Inc.

3545 John Hopkins Court, Suite 210

San Diego, CA 92121

Ladies and Gentlemen:

We have represented Regulus Therapeutics Inc., a Delaware corporation (the “Company”), in connection with the filing by 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 1,000,000 shares of the Company’s Common Stock, $0.001 par value per share (the “Shares”), issuable pursuant to the Company’s Inducement Plan (the “Plan”).

In connection with this opinion, we have examined and relied upon the Registration Statement and related prospectus, the Company’s Certificate of Incorporation and Bylaws, each as amended, the Plan, and 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 and the conformity to originals of all documents submitted to us as copies thereof.

Our opinion is expressed only with respect to the federal laws of the United States of America and the General Corporation Law of the State of Delaware. We express no opinion as to whether the laws of any particular jurisdiction other than those identified above are applicable to the subject matter hereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when sold and issued in accordance with the Plan, the Registration Statement and related prospectus, 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).

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

Sincerely,

Cooley LLP

By:	/s/ Matthew T. Browne
	Matthew T. Browne

4401 EASTGATE MALL, SAN DIEGO, CA 92121 T: (858) 550-6000 F: (858) 550-6420 WWW.COOLEY.COM