The adult magazine mogul's secretary of more than 40 years, Mary O'Connor, recently passed away and Harris has decided to honour her by raising money for a good cause.
The blonde is selling off the pink gown and shoes she wore when she exchanged vows with Hefner on New Year's Eve (31Dec12), via an auction on Charitybuzz.com.
In a post on Twitter.com, Harris writes, "I am auctioning my wedding dress... to raise money for lymphoma in memory of Mary."
A message posted on the auction website states, "Crystal is donating this dress in memory of her good friend, Mary O'Connor. Mary was Hugh Hefner's longtime assistant of 40 years, and is credited with helping Crystal reconcile with Hef last year, ultimately leading to their recent wedding. Money raised will benefit the Leukemia and Lymphoma Society in Mary's name."
The auction ends on 11 February (13).