The Czech international joined Chelsea from French club Rennes for £7m in 2004 and has made 166 appearances for the club, keeping a remarkable 90 clean sheets.
Chelsea manager Luiz Felipe Scolari added: "I am delighted that Petr has signed a new contract.
"In my view he is the best goalkeeper in the world, so I am very pleased that he will remain with me at Chelsea."
In his first season, Cech was awarded the Barclays Premiership Golden Gloves as he set a new record in top-flight football for not conceding a goal in 1,024 minutes and for the most clean sheets (21) in a single Premier League season.
He was also voted Uefa's most valuable goalkeeper in the 2005/06 season.
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