The twice-divorced Hefner, 85, and Harris were set to exchange vows in front of 300 guests Saturday at the Playboy Mansion in Los Angeles, People.com reported.
"The wedding is off," Hefner said via Twitter Tuesday. "Crystal has had a change of heart."
"I heard the sad news this morning," Harris' manager Michael Blakey told People.com. "The split was a mutual decision and the two remain good friends."
2014: The Year in Fashion [PHOTOS]
Mindy Kaling mistaken for Malala Yousafzai