Cech, who is in Prague preparing for Euro 2012 next month, has featured in more games (369) for the Londoners than any other overseas player.
"I am really happy I will be a part of this great club for another four years," he told their website.
"I hope the next four years will be as successful as the last eight."
The 30-year-old joined Chelsea from French club Stade Rennes in 2004 and quickly established himself as one of the top keepers in the Premier League.
Cech has won three Premier League titles, four FA Cups and two League Cups and saved three penalties in the shootout win over Bayern Munich in the Champions League final on May 19.
He did not play in his country's 2-1 friendly win over Israel on Saturday but is expected to feature in the Euro 2012 warmup against Hungary on June 2.
The Czechs face co-hosts Poland, Russia and Greece in Group A next month.
