PURPOSE: To prepare a siloxane-oxyalkylene copolymer suitable as a surfactant in the use of urethane foams.

CONSTITUTION: (A) an organosiloxane selected from among organohydrogensiloxanes having a mean structural formula of formula I (R is a 1-10C hydrocarbon with no aliphatic unsaturation; a has a mean value of 1-192; b has a mean value of 1-30), (B) a polyoxyalkylene selected from compounds of formula II to formula IV (R1 is an alkenyl; z is 1-20; w is 1-20),and (C) a monocarboxylate ester of an alkanediol (e.g.; 2,2,4-trimethyl-1,3- pentanediol monoisobutyrate) are mixed. The mixture is maintained at a temperature not exceeding the reacting temperature (85-130°C) by an inert gas. A noble metal hydrosilylation catalyst is added to the heated mixture, which is maintained at a temperature of lower than 130°C to recover the copolymer.