The new deal will keep the 27-year-old at the club until the summer of 2012.
Clemens joined Werder Bremen from Bayer Leverkusen in 2006.
Werder coach Thomas Schafe told Kicker.de: “Clemens took a couple of giant steps forward in the past two years.
“We welcome the fact that in the future we can take futher steps with him, because we know that he still can get better.”
