The invention provides a method for imparting releasability to the surface of a plastic film or paper by coating the surface with an organopolysiloxane composition followed by curing, in which the curing is complete by heating at a relatively low temperature and the cured surface film of the composition is very stable and free from the problem of transfer to another body in contact therewith. The composition comprises a vinyl-containing organopolysiloxane, an organohydrogenpolysiloxane and a platinum compound to catalyze the addition reaction between the silicon-bonded vinyl groups and silicon-bonded hydrogen atoms. Different from conventional organohydrogenpolysiloxane having a linear molecular structure, the organohydrogenpolysiloxane used in the invention is represented by the general unit formula (RSiO.sub.1.5).sub.m (RHSiO.sub.0.5).sub.n, in which R is a monovalent hydrocarbon group free form unsaturation and m and n are each a positive integer with the proviso that the ratio of n/m is from 0.1 to 3.0, or a combination thereof with a linear organohydrogenpolysiloxane.