Masato Kai (甲斐 優斗, Kai Masato, born 25 September 2003) is a Japanese male volleyball player and an Olympian.

He plays as an outside hitter for the Japan men's national volleyball team.

Masato Kai has an older brother, Kotaro Kai, who also plays volleyball.

Kai was chosen to represent Japan as one of their players for the 2024 Summer Olympics.

This biographical article relating to volleyball in Japan is a stub.