The present invention has for its object to provide a polymer available upon coupling of polymers of radical-polymerizable olefin monomer or monomers and a process for producing said polymer. The present invention is concerned with a method for effecting polymer-polymer coupling in the living radical polymerization of a radical-polymerizable olefin monomer which comprises adding a compound having at least two sparingly radical-polymerizable alkenyl groups during or after polymerization.