Kenji Watanabe (渡辺 健司, Watanabe Kenji, July 17, 1969 – September 18, 2017) was a Japanese breaststroke swimmer.

He represented his native country in three consecutive Summer Olympics, starting in 1984.

He was the grandson of Hisakichi Toyoda, who won a gold medal in the 4 × 200 m freestyle in the 1932 Summer Olympics.

Watanabe again won gold in the 200m breaststroke at the 1990 Asian Games in Beijing.

He also won silver medals in the 100m breaststroke and the 4 × 100 m medley relay.