Richard Gere and Charlize Theron were amongst the stars voicing their opinions against Bush at the Venice Film Festival.
Gere was promoting his new film The Hunting Party - in which he plays a reporter determined to track down the man who is charged with crimes against humanity during the Bosnian war - when he spoke out against the current US president.
"How did we elect Bush twice?" Gere explained at a news conference on Monday. "What's interesting to me is how do the bad people among us end up our leaders?"
Meanwhile Theron plays a New Mexico detective investigating the case of a US soldier who disappears after returning from fighting in Iraq in The Valley of Elah.
"The decision-making process for going into Iraq was very hastily done and I think the facts weren't there and I just don't think you go to war for those reasons," Theron, 32, said in an interview. "I think the thing that upset me most was the manipulation that our government did towards our people, manipulating them to believe that if they weren't for the war, they weren't patriotic."
The film festival ends Saturday with the awarding of the top Golden Lion prize.