The particle sizes and their size distributions of latexes from the dispersion polymerization of styrene using a small amount of omega-methoxy poly(ethylene oxide)(n) undecyl-alpha-methacrylate macromonomer (PEO-R-MA-40) as a polymerizable stabilizer in ethanol-water media have been studied. Monodisperse or/and nearly monodisperse latex particles from 0.1 to 1 mu m in diameter were readily obtained. The diameter of latex particles follows the relationship D-vad proportional to theta(0.33) [PEO-R-MA-40](o)(-0.60) [styrene](o)(1.02) [AIBN](o)(-0.09), where theta is the fractional conversion of styrene. Except for the styrene concentration dependency, this relationship is in excellent agreement with the model developed by Paine(11) and modified by Kawaguchi et al.(13). When the surface composition of the grafted PEO macromonomer on the latex particles exceeded 16% as analyzed by X-ray photoelectron spectroscopy (XPS), the particles were nearly monodisperse. In terms of polymerization, this occurred around 18% conversion of styrene. Beyond this critical state of polymerization, the latex particles grew bigger with more PEO macromonomer-styrene copolymers situated on the particle surface. The effect of various factors on the particle size distribution is also discussed.