Koutaro Nishiyama
- Title: Koutaro Nishiyama
- Popularity: 3.83
- Known For: Acting
- Birthday: 1991-10-11
- Place of Birth: Kanagawa, Japan
- Homepage: http://www.81produce.co.jp/actor_search/index.php/item?id=98
- Also Known As: Kotaro Nishiyama, 西山 宏太朗, Kōtarō Nishiyama, Koutarou Nishiyama