Rubber vulcanizates having excellent oil resistance, heat resistance and cold resistance can be obtained from a rubbery copolymer which is a polymerization product of an acrylic monomer mixture of which the essential components are an organosiloxy-containing acrylate compound such as acryloxymethyl pentamethyl disiloxane and 3-acryloxypropyl pentamethyl disiloxane and an epoxy group- or halogen-containing monomer such as allyl glycidyl ether, glycidyl methacrylate and vinyl chloroacetate, optionally, with addition of an acrylate ester monomer such as ethyl acrylate, n-butyl acrylate and 2-methoxyethyl acrylate.