A curable rubber composition comprising a curable organopolysiloxane or perfluoropolyether group-containing organosilicon compound, a curing agent, and a silica filler having a mean particle size of 0.001-10 m is cured into a cured rubber. For improving compression set, the cured rubber is post treated with a hydrolyzable aminosilane or amidosilane having a Si—N bond in vapor form.