An organopolysiloxane composition which contains from 0.01% to less than 0.5% by weight of a sulfidable metal powder is provided. When a silver-containing precision electronic part is encapsulated or sealed with the cured composition, the metal powder in the cured composition is sulfided with sulfur-containing gas, thereby preventing or retarding the corrosion of the encapsulated or sealed electronic part with the sulfur-containing gas.