Christie's auction house says it will be selling 110 of the actor's guitars on Oct. 11.
Gere said he is parting with the guitars to support humanitarian causes around the world.
The auction house said Gere studied trumpet and that the actor is also a self-taught pianist and guitarist.
Gere said he never planned to put together a guitar collection and bought only ones he liked and that sounded good to him.
Among the instruments for sale are brands C.F. Martin, Gibson, Fender, Gretsch and Epiphone, and guitars once owned by blues guitar artist Albert King and reggae musician Peter Tosh.
In addition to the guitars, amplifiers will also be sold.
The sale is expected to bring $1 million.
The Associated Press contributed to this report.