Australian opposition leader Tony Abbott backpedalled after derogatory comments about the clothes and appearance of Julia Gillard, the country's first female prime minister.

The furore began when well-known Australian feminist Germaine Greer told ABC television that Gillard wore unflattering jackets and had a "big arse".

"Every time she turns round, you've got that strange horizontal crease, which means they're cut too narrow in the hips," Greer said.

"You've got a big arse, Julia. Just get on with it."

While meeting the public at a community forum on Thursday the issue came up and Abbott responded: "I know, I know, I know. Germaine Greer was right on that subject."

On Friday he said he regretted the remark after it was widely played on television.

"It was an off-the-cuff remark responding to an observation of a member of the public and I shouldn't have said it and I regret it," he said.

Gillard is Australia's first female leader and her boyfriend Tim Mathieson has previously hit out at people "bullying" her.

"Being a woman, I think she's gets targeted quite a bit by the big boys in town," he said at the time.

"Bullying women just doesn't work for me... calling females names does not get you anywhere," he added.