A curable composition and a method of rendering a base material or a shaped item antifouling comprising coating or impregnating a surface of the base material with the curable composition comprising (A) an organopolysiloxane having functional groups capable of condensation reaction at both molecular terminals thereof and (B) a hydrophobic silica wherein the hydrophobic silica (B) is thermally treated together with the organipolysiloxane (A).