A copolymer of (i) an alkyl acrylate or alkyl methacrylate and (ii) a hydroxyalkyl acrylate or hydroxyalkyl methacrylate is used as a secondary protective colloid in the suspension polymerization of vinyl chloride monomer. The alkyl group of the alkyl acrylate or alkyl methacrylate is preferably a 2-ethylhexyl group. The hydroxyalkyl group of the hydroxyalkyl acrylate or hydroxyalkyl methacrylate is preferably a hydroxyethyl group.