Vinylbenzyl-terminated poly(acrylic acid) (PAA) macromonomers were prepared by the use of a free radical polymerization technique. The polymer microspheres were synthesized by emulsion copolymerization of methyl methacrylate (MMA) with PAA macromonomers in an aqueous or 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, macromonomer concentration, and macromonomer molecular weight increased. It was remarkable that the diameter of the polymer microspheres depended strongly on the pH in the solvent medium.