Water-repellent gypsum compositions of components (A) 100 parts by weight of gypsum (B) 0.05-50 parts by weight of oxide and/or hydroxide or alkali and/or alkaline earth metals (C) 0.05-20 parts by weight of glycol-functional siloxane mixture, preparable by the reaction of 1 mole of alkyltrihalosilane or alkyltrialkoxysilane with at least 2.5 moles of a glycol or mixture of glycols, exhibit water repellancy similar to gypsum which has been hydrophobed with H-siloxane.