Polystyrene particles were. polymerized at neutral medium (pH 7)for electro-phoretic particles that can be moved in dielectric medium by electric field. The poly(ethylene glycol) methyl ether methacrylate (PEG-MMA) and methacrylic acid. (MA) men, used as surface charge-generating comonomers. The zeta potentials of three kinds of polystyrene particles were measured, in. dielectric medium. by means of ELS-8000 dynamic light scattering. As PEG-MMA concentration increased, the zeta potential became higher The highest zela potential of polymer surface was measured to be about 188 mV at a polymer of PEG-MMA 5 mol% relative to styrene. However, as the ratio of [MA]/[PEG-MMA] increased, the zeta potential, and electrophoretic mobility of the PS particles decreased.