Abstract: A novel method is proposed for the preparation of a curable organopolysiloxane composition which is suitable as a material of a mold-making having excellent mechanical properties and durability in use for replica molding. The method comprises (a) blending a vinyl-containing organopolysiloxane with a hydrophobic reinforcing silica filler and hexamethyl disilazane, optionally, together with water each in a limited amount, (b) subjecting the blend to a heat treatment and (c) admixing the heat-treated blend with an organohydrogenpolysiloxane as a crosslinking agent of the vinyl-containing organopolysiloxane and a platinum compound as a catalyst for promoting the addition reaction between the silicon-bonded vinyl groups and the silicon-bonded hydrogen atoms.