Well-defined poly(methacrylic acid) (PMA) macromonomers having one vinylbenzyl group per polymer chain were prepared by the use of the living anionic polymerization technique. The polymer microspheres were synthesized by emulsion copolymerization of methyl methacrylate (MMA) with PMA macromonomers in an aqueous ethanol solution. In this copolymerization system, the macromonomer acted not only as a comonomer but also as a stabilizer. The diameter of the polymer microspheres decreased as the water fraction in the mixed solvent increased. The polymer microspheres that were produced had a very narrow particle size distribution.