Klaasen is a surname. Notable people with the surname include:
Berton Klaasen (born 1990), South African rugby union player
Heinrich Klaasen (born 1991), South African cricketer
Jelle Klaasen (born 1984), Dutch darts player
Lorraine Klaasen, Canadian musician
Raven Klaasen (born 1982), South African tennis player
Robert Klaasen (born 1993), Dutch footballer
Thandi Klaasen (1931–2017), South African musician