Exhibit 5.1

210 Park Avenue, Suite 2300 Oklahoma City, Oklahoma 73102 405-930-5151 Fax 405-212-5843 www.steptoe-johnson.com

December 18, 2024

Perma-Fix Environmental Services, Inc.

8302 Dunwoody Place, Suite 250
Atlanta, Georgia 30350

Ladies and Gentlemen:

We have acted as counsel to Perma-Fix Environmental Services, Inc., a Delaware corporation (the “Company”), in connection with the issuance and sale by the Company of an aggregate of (i) 2,530,000 shares (the “Shares”) of the Company’s common stock, par value $0.001 per share (the “Common Stock”), pursuant to the Underwriting Agreement, dated December 18, 2024 (the “Underwriting Agreement”), among the Company and Craig-Hallum Capital Group LLC, as underwriter (the “Underwriter”) and (ii) warrants to purchase up to 126,500 shares of Common Stock to the Underwriter and certain of its designees (the “Underwriter Warrants”). The foregoing number of Shares includes 330,000 shares of Common Stock being sold pursuant to the exercise by the Underwriter of an option to purchase additional Shares.

In arriving at the opinions expressed below, we have reviewed the following documents:

(a) the Underwriting Agreement;

(b) the Registration Statement on Form S-3 (Registration No.333-283555), filed by the Company under the Securities Act of 1933, as amended (the “Securities Act”), with the Securities and Exchange Commission (the “Commission”) on December 2, 2024 and declared effective on December 12, 2024, including the exhibits thereto and the documents incorporated by reference therein to and including the date of the Underwriting Agreement (the “Registration Statement”); and

(c) copies of the Restated Certificate of Incorporation, as amended, and the Second Amended and Restated Bylaws of the Company, as amended through the date hereof.

We have considered such matters of law and fact, and relied upon such certificates of officers of the Company and public officials, corporate records and other information furnished to us, including without limitation the certificates and representations referred to below, as we have deemed appropriate as a basis for the opinion set forth below.

West Virginia • Ohio • Kentucky • Pennsylvania • Texas • Colorado • Oklahoma

Perma-Fix Environmental Services, Inc.

December 18, 2024

Page 2

In arriving at the opinion expressed below, we have assumed the authenticity of all documents submitted to us as originals, the conformity to the originals of all documents submitted to us as copies and the genuineness of all signatures. In addition, we have assumed and have not verified (i) the accuracy as to factual matters of each document we have reviewed and of the representations and warranties set forth therein and (ii) that the Underwriting Agreement is a legal, valid and binding obligation of each party thereto, other than the Company, enforceable against each such party in accordance with its terms.

Based on and subject to the foregoing, and to the other assumptions, qualifications and limitations set forth herein, it is our opinion that:

(i) the Shares have been duly authorized by the Company and, when issued, delivered, and paid for in accordance with the Underwriting Agreement, will be validly issued, fully paid and non-assessable;

(ii) the Underwriter Warrants, when issued, delivered, and paid for in accordance with the Underwriting Agreement, will constitute valid and binding obligations of the Company, enforceable against the Company in accordance with their terms; and

(iii) the shares of Common Stock issuable upon exercise of the Underwriter Warrants, when issued and paid for pursuant to the Representative Warrants, will be duly authorized and validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the laws of the State of New York and the Delaware General Corporation Law as in effect on the date hereof, and we express no opinion as to the effect of the laws of any other jurisdiction or as of any later date.

This opinion letter speaks only as of the date hereof, and we disclaim any obligation to advise you of changes of law or fact that occur after the date hereof.

We hereby consent to the filing of this opinion with the Commission to make it an exhibit to the Registration Statement and we further consent to the use of our name under the caption “Legal Matters” in the forms of prospectus, preliminary prospectus supplement, and final prospectus supplement relating to the offering of the Shares included in the Registration Statement or filed by the Company pursuant to Rule 424(b) under the Securities Act. In giving this consent, we do not hereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Steptoe & Johnson PLLC

STEPTOE & JOHNSON PLLC