Exhibit 5.1 SIDLEY AUSTIN LLP BEIJING HONG KONG SAN FRANCISCO 1 BOSTON HOUSTON SHANGHAI BUILDING 1 BRUSSELS LONDON SINGAPORE PALO ALTO, CA 94304 CENTURY CITY LOS ANGELES SYDNEY +1 CHICAGO MUNICH TOKYO +1 FAX DALLAS NEW YORK WASHINGTON, D.C. GENEVA PALO ALTO FOUNDED 1866 April 5, 2017 Celsion Corporation 997 Lenox Drive, Suite 100 Lawrenceville, NJ 08648 Re: Registration Statement on Form S-1 Ladies and Gentlemen: We refer to the Registration Statement on Form S-1 filed on the date hereof by Celsion Corporation, a Delaware corporation (the " Company ") , with the Securities and Exchange Commission (the "