The singer and actress wore the Bob Mackie-designed black velvet and lace dress to this year's Golden Globe Awards ceremony.
Proceeds from the auction will go to expand efforts already under way to provide stable, structured education to Haiti's children living in tent cities following January's devastating earthquake.
The auction started Tuesday and will run through May 14 at www.ebay.com/chergives. Cher has included a handwritten note on her personal note card for the winner to ensure the authenticity of the gown.
"I am honored to support the victims of the Haiti earthquake," Cher said in a statement Wednesday. "These schools provide education and emotional support for the children hardest hit by the recent disaster."
The Voila Foundation said it has donated $50,000 to support the efforts of PRODEV, a Haitian organization that has already built and staffed 14 tent-city schools in Haiti.
Voila said it also has committed to match any money raised by the gown auction to expand those efforts.