Castex is a Gascon surname meaning "castle". Notable people with the surname include:
Alphonse Castex (1899–1969), French Olympic athlete Bertrand Pierre Castex (1771–1842) French general and viscount Françoise Castex, French Socialist MP Jean Castex (born 1965), French politician, Prime Minister of France from 2020 to 2022 Jean-Jacques Castex (1731–1822), French sculptor Louis Castex (1868–1954), French sculptor Louis Castex (1896–1968), French aviation pioneer Michel Castex (born 1943), French journalist Pierre Castex (1924–1991), French scriptwriter Pierre-Georges Castex (1915–1995), literary critic Raoul Castex, French Navy Vice Admiral (1878–1968), theorist of naval warfare