The polymer microspheres were synthesized by emulsion copolymerizations of styrene with vinyl benzyl terminated poly(methacrylic acid) (PMA) macromonomers in an aqueous ethanol solution. In these copolymerization systems, the macromonomer acted not only as a comonomer but also as a stabilizer. The particle diameters obtained from the water-soluble initiator system showed smaller values than those obtained from the water-insoluble initiator system. These polymer microspheres had a very narrow particle-size distribution. The particle diameters depended strongly on the feed amount and molecular weight of PMA macromonomers, water fraction-in the mixed solvent, and pH in the medium.