The new deal will keep the former Roma player in Turin until the end of the 2011 season.
He said: “I am honoured to have extended my contract with Juve. To wear the Bianconeri jersey for another four years is a great achievement and I am sure myself and my team-mates will soon reach important results in Italy and in Europe.
“This isn’t only a professional choice. The club, the team, the new coach and the city convinced me this was the right decision.”