Kasai (written: 河西, 葛西 or 笠井) is a Japanese surname. Notable people with the surname include:
Akira Kasai (born 1952), Japanese politician
Jun Kasai (born 1974), Japanese professional wrestler
Ken'ichi Kasai, (born 1970), Japanese anime director
Kenta Kasai (born 1985), Japanese football player
Kimiko Kasai (born 1945), retired Japanese jazz singer
Masae Kasai (1933–2013), former Japanese volleyball player
Noriaki Kasai (born 1972), Japanese ski jumper
Tomomi Kasai (born 1991), Japanese singer, actress and a former member of the idol group AKB48
Yoshiko Yoshiizumi nee Kasai (born 1980), Japanese ski jumper
Zenzō Kasai (1887-1928), Japanese novelist active in the Taishō period
