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