Exhibit 5.1

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FOX ROTHSCHILD LLP

Princeton Pike Corporate Center

997 Lenox Drive

Lawrenceville, NJ 08648-2311

August 24, 2018

BIO-key International, Inc.

3349 Highway 138, Building A, Suite E

Wall, NJ 07719

Ladies and Gentlemen:

We have acted as counsel to BIO-key International, Inc., a Delaware corporation (the “Company”), in connection with the sale by the Company of an aggregate of 1,380,000 units (the “Units), each consisting of one share of common stock, par value $0.0001 per share (the “Common Stock”), and a warrant to purchase 0.75 shares of Common Stock (the “Warrants” and together with the Common Stock, the “Offering Securities”) to purchase shares of Common Stock, pursuant to that certain Underwriting Agreement, dated as of August 22, 2018 (the “Underwriting Agreement”), by and among the Company and the underwriters named in Schedule I to the Underwriting Agreement, for whom Maxim Group LLC is acting as representative.

In connection with the offering and sale of the Offering Securities, the Company has prepared and filed with the Securities and Exchange Commission (the “Commission”) (i) a registration statement on Form S-3 (File No. 333-225934) (as amended, the “Registration Statement”), (ii) a base prospectus dated July 6, 2018 (the “Base Prospectus”), (iii) a preliminary prospectus supplement dated August 21, 2018 filed with the Commission pursuant to Rule 424(b) under the Securities Act of 1933, as amended (the “1933 Act”), including any documents incorporated therein by reference (the “Preliminary Prospectus”), and (iv) a prospectus supplement dated August 23, 2018 filed with the Commission pursuant to Rule 424(b) under the 1933 Act, including any documents incorporated therein by reference (the “Prospectus Supplement” and together with the Base Prospectus, the “Offering Prospectus”).

In acting as counsel for the Company and arriving at the opinions expressed below, we have examined the Underwriting Agreement, the Registration Statement, the Preliminary Prospectus, and the Offering Prospectus as well as the charter and bylaws of the Company as in effect on the date hereof. We also have examined and relied upon the originals, or copies certified or otherwise identified to our satisfaction, of such records, documents, certificates and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below.

In rendering this opinion, we have assumed the genuineness and authenticity of all signatures on original documents; the legal capacity of all natural persons; the authenticity of all documents submitted to us as originals; the conformity to originals of all documents submitted to us as certified or photocopies; the authenticity of the originals of such latter documents; the accuracy and completeness of all documents and records reviewed by us; the accuracy, completeness and authenticity of certificates issued by any governmental official, office or agency and the absence of change in the information contained therein from the effective date of any such certificate; and the due authorization, execution and delivery of all documents where authorization, execution and delivery are prerequisites to the effectiveness of such documents.

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As to questions of fact relevant to this opinion, without any independent investigation or verification, we have relied upon, and assumed the accuracy of, the representations and warranties of each party as to factual matters in the Underwriting Agreement, and have relied upon certificates of officers of the Company and written statements of certain public officials.

Based upon and subject to the foregoing, and the qualifications and limitations set forth below, it is our opinion that:

In addition to the qualifications and limitations set forth above, the opinions expressed herein are subject to the following qualifications and limitations:

(a)     We express no opinion with respect to laws other than those of the State of New York and the Delaware General Corporation Law as in effect on the date hereof, and we assume no responsibility as to the applicability thereto, or the effect thereon, of the laws of any other jurisdiction.  We are not rendering any opinion as to compliance with any federal or state law, rule or regulation relating to securities, or to the sale or issuance thereof.

(b)     To the extent that the opinions given above relate to the enforceability of any agreement or other document referred to herein, the opinions are subject to, and we give no opinion with respect to, the effect of applicable bankruptcy, insolvency, fraudulent conveyance, fraudulent transfer, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally and by general equitable principles (regardless of whether enforcement is sought in equity or at law), including, without limitation, principles regarding good faith and fair dealing.

(c)     We express no opinion as to the enforceability of (i) provisions relating to the availability of specific remedies or relief, including indemnification and contribution, or the release or waiver of any remedies or rights or time periods in which claims are required to be asserted, (ii) provisions that allow cumulative remedies, late charges or default interest, (iii) provisions stating that amendments, waivers or modifications may only be in writing, to the extent that an oral agreement or an implied agreement by course of conduct may be created that modifies such a provision or (iv) provisions relating to choice of law or forum.

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We hereby consent to the filing of this opinion as an exhibit to the Company’s Current Report on Form 8-K dated August 24, 2018, which is incorporated by reference in the Registration Statement and to the use of our name wherever it appears in the Registration Statement, the Base Prospectus, the Prospectus Supplement, and in any amendment or supplement thereto. In giving such consent, we do not hereby admit that we are within the category of persons whose consent is required under Section 7 of the 1933 Act or the rules and regulations of the Commission thereunder. This opinion speaks only as of the date above written, and we hereby expressly disclaim any duty to update any of the statements made herein or to advise you of any subsequent changes in the facts stated or assumed herein or of any subsequent changes in applicable law.