Batman director Christopher Nolan says late Australian actor Heath Ledger cannot be replaced as The Joker.

Nolan says he plans to bring back Batman for another film, but The Joker - the villain played so maniacally in The Dark Knight by Ledger - will not be there.

Ledger won an Academy Award for the role a year after his death, making him only the second performer ever to earn an Oscar posthumously.

"For me, Heath was the definitive Joker," Nolan said in an interview to promote Inception, his latest sci-fi thriller.

"It wouldn't feel appropriate to readdress that character."

Ledger died of an accidental prescription drug overdose in January 2008.

His death stoked fan interest in The Dark Knight, which topped $US1 billion ($A1.14 billion) at the box office worldwide.

The next Batman film will be the third in the current Warner Bros incarnation of the franchise, which stars Christian Bale as the vigilante superhero.

Nolan would not disclose what villain or villains might feature in the film.

It is due out in 2012.

- ABC/AAP