It's their fourth Wimbledon title together, part of their haul of nine Grand Slam women's doubles championships.
"There's nothing like winning a title with your sister," said Serena, who has won 11 major singles titles. "It's really a good feeling."
Earlier Saturday on Centre Court, Serena beat Venus 7-6 (3), 6-2 in singles to win her third Wimbledon title. In each of those championships, she won it by beating Venus.
A year ago, Venus beat Serena in the championship match to win her fifth Wimbledon singles title, and the pair then teamed up to win the doubles.
"One out of two's not bad," Venus said. "I really wanted to win the singles, but they're two separate events. If I won the singles and not the doubles, it's still not the same."
Against the Australians, the Williams sisters traded breaks in the first set, with Stosur and Stubbs taking a 2-1 lead off Serena's opening service game. But the Americans eventually broke back to 4-4 when Stosur put a backhand volley into the net.
In the tiebreaker, Venus put the sisters up a mini-break on the second point with a return of serve that Stubbs couldn't get back over.
"The ball clipped the tape, and therefore it went a little bit higher than it should have and it hit my frame and didn't quite get off the string," Stubbs said. "It was really unlucky."
The most entertaining point of the match came with Stubbs serving at 1-1 in the second set. Serena returned the serve, and Stubbs swung her racket behind her and hit the ball through her legs to get it back over.
"I do that because sometimes you have to do that," said Stubbs, who added that she makes that kind of shot all the time. "That's just experience and being an idiot on the court half the time."
As the point continued, Stosur stood at the net and battered back volley after volley as both Venus and Serena grunted and groaned while sending groundstrokes back over the net.
Stosur eventually won the point with a drop shot neither sister could get near, and the Australian took that game. But the sisters broke Stubbs to go up 4-3 in that set and kept control.
"I'm really excited to have doubles titles," Serena said. "I rack 'em up."