Dunst played an immortal woman trapped in a little girl's body when she co-starred with Pitt and Tom Cruise in the 1994 movie.
"It was just a peck," Dunst, 30, said of her kiss with Pitt in an interview with Bullett magazine.
"I remember Brad would watch lots of 'Real World' episodes," she said of the now 49-year-old father of six children. "He had this long hair. He was just a hippie-ish cool dude. Everyone at the time was like, 'You're so lucky you kissed Brad Pitt,' but I thought it was disgusting. I didn't kiss anyone else until I was 16, I think. I was a late bloomer."