Frithjof Kleen (born 25 June 1983 in Berlin) is a German sailor, who specialized in two-person keelboat (Star) class. He represented Germany, along with his partner Robert Stanjek in the Star class at the 2012 Summer Olympics, and also captured a silver medal at the 2011 ISAF Sailing World Championships in Perth, Australia. Kleen has also been training throughout most of his sporting career for the North German Sailing Regatta () in Hamburg under his personal coach Alan Smith.