Koichi Sato is a Japanese actor. He is the son of veteran Japanese actor Rentarō Mikuni.

Rentarō Mikuni was a Japanese actor, writer and director, who starred in films of Keisuke Kinoshita, Mikio Naruse, Tadashi Imai, Shōhei Imamura, Tomu Uchida and many others. He received numerous prizes for his performances and was awarded the Jury Prize at the 1987 Cannes Film Festival for his film Shinran: Path to Purity, which he wrote and directed.