Well-defined poly(vinyl alcohol) (PVA) macromonomer having c. two vinylbenzyl groups at the terminal end was prepared by means of free radical polymerization. Polymer microspheres were synthesized by emulsion copolymerization of methyl methacrylate (MMA) with PVA macromonomer in aqueous ethanol solution. In this copolymerization system, the macromonomer acted as not only a comonomer but also a stabilizer. The diameter of the polymer microspheres decreases as the water fraction in mixed solvent increased. The polymer microspheres had a very narrow particle-size distribution. Subsequently, the polymer microspheres were synthesized by emulsion copolymerization of MMA with binary PVA/poly(methacrylic acid) (PMA) macromonomer blends. PMA macromonomer also possessed one vinylbenzyl group per chain. Even in these systems of binary macromonomer blends as the emulsifier, the polymer microspheres formed had a very narrow particle-size distribution. Binary macromonomers formed co-micelles with MMA monomer and acted not only as the comonomer but also as the stabilizer.