Exhibit 5.1

May 30, 2025

Imunon, Inc.

997 Lenox Drive, Suite 100

Lawrenceville, New Jersey 08648

Ladies and Gentlemen:

We have acted as counsel to Imunon, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing by the Company of a Registration Statement on Form S-1 (the “Registration Statement”), with the U.S. Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), relating to the proposed resale of up to 22,027,780 shares (the “Selling Holder Shares”) of common stock, par value $0.01 per share (the “Common Stock”), consisting of (i) 2,777,779 shares of Common Stock (the “Shares”), (ii) up to 4,444,444 shares of Common Stock (the “Pre-Funded Warrant Shares”) reserved for issuance upon the exercise of outstanding pre-funded warrants (the “Pre-Funded Warrants”), (iii) up to 14,444,446 shares of Common Stock (the “Common Warrant Shares”) reserved for issuance upon the exercise of outstanding common warrants (the “Common Warrants”), and (iv) up to 361,111 shares of Common Stock (the “Placement Agent Warrant Shares” and, collectively with the Pre-Funded Warrant Shares and the Common Warrant Shares, the “Warrant Shares”) reserved for issuance upon the exercise of outstanding placement agent warrants (the “Placement Agent Warrants” and, collectively with the Pre-Funded Warrants and the Common Warrants, the “Warrants”), by the selling securityholders listed in the Registration Statement, all of which Selling Holder Shares may be sold from time to time and on a delayed or continuous basis, as described in the prospectus that forms a part of the Registration Statement (the “Prospectus”).

In connection with this opinion, we have examined originals or copies (certified or otherwise identified to our satisfaction) of (i) the Company’s Amended and Restated Certificate of Incorporation, (ii) the Company’s Amended and Restated Bylaws, (iii) the Registration Statement and the Prospectus, (iv) the Warrants, and (v) such corporate records, agreements, documents, and other instruments, and such certificates or comparable documents of public officials or of officers and representatives of the Company, as we have deemed relevant and necessary as a basis for the opinion hereinafter set forth. In such examination, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, conformed or photostatic copies, and the authenticity of the originals of such latter documents. As to certain questions of fact material to this opinion, we have relied upon certificates or comparable documents of public officials and officers and representatives of the Company and have not sought to independently verify such facts.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that:

The opinion expressed herein is limited to the General Corporation Law of the State of Delaware and, with respect to the enforceability of the Warrants, the laws of the State of New York, and we express no opinion as to the effect on the matters covered by this opinion of the laws of any other jurisdiction. We express no opinion as to (a) any provision for liquidated damages, default interest, late charges, monetary penalties, make-whole premiums or other economic remedies to the extent such provisions are deemed to constitute a penalty, (b) consents to, or restrictions upon, governing law, jurisdiction, venue, arbitration, remedies or judicial relief, (c) waivers of rights or defenses, (d) any provision requiring the payment of attorneys’ fees, where such payment is contrary to law or public policy, (e) the creation, validity, attachment, perfection or priority of any lien or security interest, (f) advance waivers of claims, defenses, rights granted by law or notice, opportunity for hearing, evidentiary requirements, statutes of limitation, trial by jury or at law or other procedural rights, (g) waivers of broadly or vaguely stated rights, (h) provisions for exclusivity, election or cumulation of rights or remedies, (i) provisions authorizing or validating conclusive or discretionary determinations, (j) grants of setoff rights, (k) proxies, powers and trusts, (l) provisions prohibiting, restricting or requiring consent to assignment or transfer of any right or property and (m) the severability, if invalid, of provisions to the foregoing effect. Our opinions set forth above are subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other similar laws of general application affecting the rights and remedies of creditors and to general principles of equity.

This opinion letter is expressly limited to the matters set forth above, and we render no opinion, whether by implication or otherwise, as to any other matters relating to the Company, the Selling Holder Shares, the Registration Statement or the Prospectus.

We hereby consent to being named in the Registration Statement and in the Prospectus under the caption “Legal Matters” and to the use of this opinion for filing with said Registration Statement as Exhibit 5.1 thereto. In giving this consent, we do not hereby admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended, or the rules and regulations of the Commission promulgated thereunder.

Very truly yours,

/s/ Thompson Hine LLP

Thompson Hine LLP