Serena Williams and Venus Williams claimed their fourth Australian Open women's doubles title with a straight-sets win over top seeds Cara Black and Liezel Huber.

The sisters, who were the second seeds, won 6-4 6-3 to defend the title they won at Melbourne Park last year.

Serena Williams will also look to defend her singles title when she meets Justine Henin in tomorrow's final at Rod Laver Arena.

The title was the Williams sisters' 11th as a doubles partnership and their third consecutive major after winning at Wimbledon and the US Open last year.

That has created the possibility of the duo holding all four doubles grand slam titles at the same time if they win at the French Open.

"We haven't really thought that far through," Venus Williams said.

"We were talking today about how we wished we had played more when we were younger.

"We still feel like we have so much we can win and just stay focused.

"We just love being out there and we love the competition. More than anything, we really have fun. We'll smile and we enjoy it."

Venus Williams was left slightly red-faced when she did not realise they had won until her sister told her.

Serena immediately celebrated while Venus calmly prepared for another game.

"I actually didn't know the score," she admitted.

"I thought that it was 5-2. I really don't know how I lost track.

"I thought, 'She's really happy about this break. I've never seen her this happy. But I'll go with it'."

Serena added: "I thought, okay, this is exciting we defended our title and she was like, What's going on?

"I'm like, 'The match is over. We're done now'."