Deadline.com reports Cohen had his tickets for the Oscars pulled over concerns he would turn Hollywood's biggest bash into a publicity stunt.
"Unless they're assured that nothing entertaining is going to happen on the red carpet, the Academy is not admitting Sacha Baron Cohen to the show," an insider told the website.
Cohen reportedly planned to turn up to the event as The Dictator, but change into a suit for the ceremony.
Cohen is a star in Martin Scorcese's Hugo, which is up for several Oscar awards.
He is known for pulling humiliating stunts in character, including landing upside down and trouserless in rapper Eminem's lap at the 2009 MTV Movie Awards while dressed as Bruno.
The Academy Awards is known for its serious tone, but stunts have been pulled before.
South Park creators Matt Parker and Trey Stone cross dressed in 2000, while Ben Stiller appeared in an Avatar costume in 2010.
Watch the trailer for The Dictator:
- Herald online