Filed pursuant to Rule 424(b)(3)

Registration No. 333-187466

PROSPECTUS SUPPLEMENT NO. 6

(to Prospectus dated July 21, 2013)

5,369 Shares of Series C 8% Convertible Preferred Stock

(and 2,753,348 Shares of Common Stock Underlying the Series C 8% Convertible Preferred Stock)

Warrants to Purchase up to 2,753,348 Shares of Common Stock

(and 2,753,348 Shares of Common Stock Issuable From Time to Time Upon Exercise of Warrants)

This prospectus supplement modifies and supplements the prospectus of Oxygen Biotherapeutics, Inc. (the “Company”) dated July 21, 2013 (as supplemented on July 25, 2013, July 31, 2013, August 13, 2013, August 23, 2013 and August 26, 2013) relating to 5,369 shares of Series C 8% Convertible Preferred Stock (and 2,753,348 shares of common stock issuable upon conversion of the Series C 8% Convertible Preferred Stock) and warrants exercisable for 2,753,348 shares of common stock at an exercise price of $2.60 per share (and 2,753,348 shares of common stock issuable upon exercise of the warrants).

This prospectus supplement should be read in conjunction with, and may not be delivered or utilized without, the prospectus. This prospectus supplement is qualified in its entirety by reference to the prospectus, except to the extent that the information in this prospectus supplement supersedes the information contained in the prospectus.

This prospectus supplement includes the attached Quarterly Report on Form 10-Q for the quarterly period ended July 31, 2013, as filed with the Securities and Exchange Commission (the “SEC”) on September 17, 2013.

NEITHER THE SEC NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED THESE SECURITIES OR PASSED UPON THE ADEQUACY OR ACCURACY OF THIS PROSPECTUS SUPPLEMENT. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus supplement is September 17, 2013.