A simple technique was developed to produce micron-sized, highly monodisperse polystyrene particles in single stage polymerization in aqueous media. Polymerization was carried out in a reaction system of styrene/K2S2O8/water, to which an amphoteric surfactant, dimethyldodecylbetaine, was added at different reaction times. This polymerization procedure could produce particles with an average diameter of 2 mu m and a coefficient of variation of particle size distribution of 3.4% which is much smaller than the typical monodispersity criterion of 10%.