The Williams sisters were on the verge of becoming the first tennis players with four Olympic gold medals.
They had won the Olympic doubles gold medal twice before and had each won one Olympic singles gold medal.
Andrea Hlavackova and Lucie Hradecka stood in their way in a rematch of the doubles final at Wimbledon.
But with two breaks - one in the opening game, one midway through the second set - the Williamses won.
Venus Williams finished it off with a big volley winner, winning the Americans yet another gold medal.
Across the way, Maria Kirilenko and Nadia Petrova beat Liezel Huber and Lisa Raymond for the bronze medal.
The Russians, the Americans and the Czechs displayed their Olympic medals to a packed Centre Court crowd.
The Williams sisters' first two Olympic doubles triumphs came at Sydney in 2000 and at Beijing in 2008.
Unlike in the singles medal ceremony, this time the US flag stuck around for the Star-Spangled Banner.
The Czech team had taken out the other US pair in the field, Liezel Huber and Lisa Raymond, in the semis.
Andrea Hlavackova and Lucie Hradecka sported some flashy footwear during Sunday afternoon's medal ceremony.
And perhaps the photo of the tournament...
In the mixed doubles final Victoria Azarenka and Max Mirnyi squared off with Laura Robson and Andy Murray.
Victoria Azarenka, the World No.1 in singles, and Max Mirnyi, the World No.1 in doubles, were the top seeds.
The two teams met at the net after Victoria Azarenka and Max Mirnyi scored a 26 63 108 match tie-break win.
Elsewhere, Christopher Kas and Sabine Lisicki of Germany were playing the mixed doubles bronze medal match.
But Mike Bryan and Lisa Raymond were too tough, defeating Christopher Kas and Sabine Lisicki, 63 46 104.
Mike Bryan and Lisa Raymond brought another medal home for the US. It was Lisa Raymond's first Olympic medal.
Great Britain's own Laura Robson also collected her first Olympic medal and showed it off to the fans.
Gold for Belarus, silver for Great Britain and bronze for the US - 2012's Olympic mixed doubles medalists.