Kosuke Kitajima (北島 康介, Kitajima Kōsuke^?, born September 22, 1982 in Tokyo) is a Japanese multiple Olympic gold medalist breaststroke swimmer. He won gold medals for the men's 100 m and 200 m breaststroke at both the Athens 2004 and Beijing 2008 Olympics.

Kitajima is a decorated swimmer in the world championships and was the world record holder in the 100 m breaststroke that he set in the 2008 Beijing Olympics – this mark has since been bettered by Brenton Rickard. He is also bronze medal winner in the same Olympics in the 4×100 m medley relay. He edged out his main rival Brendan Hansen who finished fourth while Kitajima won the gold medal and set the new world record.

He received four gold medals and two bronze medals in 2004 and 2008 Olympics.

His most significant rival in the breaststroke was the American swimmer Brendan Hansen. They dueled at events such as the 2005 World Championships, 2004 Summer Olympics and 2003 World Championships. Kitajima set both world records for 100 m and 200 m breaststroke in the latter occasion. Later his best in 200 m was overcome by Dimitri Komornikov and then by Hansen, who also broke Kitajima's record in the 100 m. Kitajima regained the world record (58.91) in the 100 m at the 2008 Summer Olympics. Kitajima regained the 200 m breaststroke world record in June 2008 at the Japan Open. His time of 2:07.51 shaved nearly a second off the previous record of 2:08.50 set by Hansen in 2006.