James Cameron's blockbuster was snubbed in favour of his ex-wife Kathryn Bigelow's war drama The Hurt Locker at last month's (Mar10) Academy Awards.
And Lang, who played Colonel Miles Quaritch in the biggest grossing movie of all time, is still fuming over the decision.
He tells British TV show Live From Studio Five, "We were kind of prepared for it. I was slightly disgusted, I would say, but I saw every picture that was nominated and they're all marvellous pictures. If I happen to think Avatar is the best of the lot you can forgive me for that.
"I would never want to in any way disrespect another film or director but having said that, we should have won."
Lang isn't the only Avatar star to voice his anger over the Oscars results - earlier this month (Apr10), Sigourney Weaver launched a scathing attack on Academy Awards bosses, insisting Cameron should have won the Best Director prize instead of Bigelow. Avatar won prizes for Best Art Direction, Best Cinematography and Best Visual Effects at the annual ceremony.