Iwai (written: 岩井 lit. "rock well" or 岩居) is a Japanese surname. Notable people with the surname include:
Atsuhiro Iwai (born 1967), Japanese footballer
Iwai Hanshirō I (1652–1699), Japanese kabuki artist
Iwai Hanshirō V (1776–1847), Japanese kabuki artist
Iwai Hanshirō VIII (1829–1882), Japanese kabuki artist
Katsuhito Iwai (born 1947), Japanese economist
Shunji Iwai (born 1963), Japanese film director
Toshio Iwai (born 1962), Japanese artist
Yukiko Iwai (born 1972), Japanese voice actress
Yukiko Iwai (Onyanko Club) (born 1968), Japanese pop singer