Bush, who plays for the New Orleans Saints, said in a statement issued through the team he is bowing to pressure from a four-year NCAA investigation that saw USC hit with heavy penalties, in making his decision to relinquish college football's top individual award.
Bush was found by NCAA investigators to have taken improper gifts from a sports agent.
Citing the sacrifices made by his USC teammates that made his winning of the Heisman possible, Bush said, "It is for these reasons that I have made the difficult decision to forfeit my title as Heisman winner of 2005."
He added: "The persistent media speculation regarding allegations dating back to my years at USC has been both painful and distracting. In no way should the storm around these allegations reflect in any way on the dignity of this award, nor on any other institutions or individuals."
USC was sanctioned by the NCAA for violations in its football program, including a two-year bowl ban, a reduction of scholarships and a forfeiture of victories, including its national championship game win over Oklahoma in the 2005 Orange Bowl.