The actress, who played a label-obsessed character in Aisha, will be wearing an international design, The Times of India reports.
A source told the newspaper: "Sonam is all set to sport a vintage look at Cannes 2011. She swears by vintage clothing and she is thinking about sporting the '20s & '50s look."
Kapoor, who is due to appear at the event as brand ambassador for L'Oreal Paris, said that her look is more of a priority than watching film screenings.
"It has always been my dream to walk the red carpet at Cannes and it is soon going to be a reality thanks to L'Oreal Paris," she said. "I look forward to meeting actors and filmmakers from the world over and attending screenings of some interesting films.
"But what excites me the most is meeting the L'Oreal Paris international dream team of make-up artistes and seeing how they transform me for one of the most glamorous red carpets in the world."
The theme of this year's event is reported to be gold. Kapoor ran into controversy last year when she was dropped from the 2010 festival at the last minute.