Kozai may refer to:
Kozai-Lidov mechanism, a dynamical phenomenon in celestial mechanics 3040 Kozai, an asteroid
Persons with the surname Kozai Yoshihide Kozai (1928–2018), Japanese astronomer Kazuteru Kozai (born 1986), Japanese badminton player Kaori Kozai (born 1963), Japanese singer Takeshi Kozai (1974–2006), Japanese judoka
See also Kosai (disambiguation) Kōzai Station