PURPOSE: Chlorinated polyolefin is dispersed in an aqueous medium containing a specific surface active agent, preferably further in the presence of oxygen, then vinyl chloride monomer is fed and the polymerization is effeced in the presence of a radical catalyst to produce title polymer with high impact strength.

CONSTITUTION: A chlorinated polyolefin as chlorinated polyethylene or chlorinated polypropylene is dispersed in an aqueous medium containing at least one surface active agent selected from the group consisting of polyoxyethylene alkyl phenyl ethers, alkylsulfate ester salts, alkylsulfosuccinate salts and alkylaryl sulfate salts, preferably in the presence of oxygen with a partial pressure of 3W30 mm Hg and then vinyl chloride monomer or a monomer mix thereof with other copolymerizable monomers is polymerized in the presence of a radical intiator to produce said polymer.