Abstract: An addition-curing organopolysiloxane composition which has excellent shelf stability around room temperature, rapidly cures by moderate ultraviolet irradiation or heating, and is suitable for use as the one solution type. A reaction inhibitor is added to the composition comprising an alkenylated organopolysiloxane, an organohydrogenpolysiloxane, and a platinum catalyst. The inhibitor is a thiophene compound, an isocyanide compound, a cyclic thioether compound, a cyclic azo ether compound, an imino compound, or a polymer which has, in the molecule, functional groups each containing one or more sulfur, nitrogen, or phosphorus atoms and has an average molecular weight of 1,000 to 200,000, and which is capable of forming a complex with a platinum atom.