Kasai (written: 河西, 葛西 or 笠井) is a Japanese surname. Notable people with the surname include:
Akira Kasai (born 1952), Japanese politicianJun Kasai (born 1974), Japanese professional wrestlerKen'ichi Kasai, (born 1970), Japanese anime directorKenta Kasai (born 1985), Japanese football playerKimiko Kasai (born 1945), retired Japanese jazz singerMasae Kasai (1933–2013), former Japanese volleyball playerNoriaki Kasai (born 1972), Japanese ski jumperTomomi Kasai (born 1991), Japanese singer, actress and a former member of the idol group AKB48Yoshiko Yoshiizumi nee Kasai (born 1980), Japanese ski jumperZenzō Kasai (1887-1928), Japanese novelist active in the Taishō period