Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the use, in the Prospectus constituting a part of this Registration Statement on Form S-1, of our report dated April 17, 2018 (which report expresses an unqualified opinion and includes an explanatory paragraph expressing substantial doubt about the Company’s ability to continue as a going concern), relating to the financial statements of Mateon Therapeutics, Inc. included in the Annual Report on Form 10-K for the year ended December 31, 2017.

We also consent to the reference to us under the caption “Experts” in the Prospectus.

/s/ OUM & CO. LLP

San Francisco, California

June 13, 2018