Exhibit 5.1

  250 West 55th Street
New York, NY 10019-9601 Telephone: 212.468.8000 Facsimile: 212.468.7900 www.mofo.com morrison foerster llp beijing, berlin, brussels, denver,
hong kong, london, los angeles,
new york, northern virginia,
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san francisco, shanghai, singapore,
tokyo, washington, d.c.

February 12, 2016

Great Ajax Corp.
9400 SW Beaverton-Hillsdale Hwy, Suite 131

Beaverton, Oregon 97005

Re: Great Ajax Corp. — Registration Statement on Form S-3

Ladies and Gentlemen:

This opinion is furnished to you in connection with the Post-Effective Amendment on Form S-3 to the Registration Statement on Form S-11 (File No. 333-203048) (the “Registration Statement”) filed by Great Ajax Corp., a Maryland corporation (the “Company”), on the date hereof, with the Securities and Exchange Commission (the “Commission”) in connection with the registration under the Securities Act of 1933, as amended (the “Securities Act”), of the resale of 10,000,740 shares of the Company’s common stock, $0.01 par value per share (the “Shares”).

In connection with this opinion, we have examined such corporate records, documents, instruments, certificates of public officials and of the Company and such questions of law as we have deemed necessary for the purpose of rendering the opinions set forth herein.

In such examination, we have assumed the genuineness of all signatures and the authenticity of all items submitted to us as originals and the conformity with originals of all items submitted to us as copies.

Based on the foregoing, we are of the opinion that the Shares are duly authorized, validly issued, fully paid and non-assessable.

Please note that we are opining only as to the matters expressly set forth herein, that no opinion should be inferred as to any other matter. We are opining herein as to the Maryland General Corporation Law as in effect on the date hereof, and we express no opinion with respect to any other laws, rules or regulations. This opinion is based upon currently existing laws, rules, regulations and judicial decisions, and we disclaim any obligation to advise you of any change in any of these sources of law or subsequent legal or factual developments which might affect any matters or opinions set forth herein.

Great Ajax Corp.

February 12, 2016

Page Two

We hereby consent to the reference to our firm under the caption “Legal Matters” in the Prospectus and to the filing of this opinion as Exhibit 5.1 to the Company’s Registration Statement. In giving such consent, we do not hereby admit that we are acting within the category of persons whose consent is required under Section 7 of the Securities Act or the rules or regulations of the Commission thereunder.

Very truly yours,

/s/ Morrison & Foerster LLP

Morrison & Foerster LLP