A method was developed for producing micrometer-sized, highly monodisperse polystyrene particles in single stage polymerization in aqueous media. The method employs an amphoteric surfactant, dimethyldodecylbetaine, that is added to the reaction system of styrene/K2S2O8/water in early stage of reaction. Polymerizations were carried out over a range of initiator concentrations (4-8 mmol/dm(3) H2O). The polymerization procedure could produce particles with an average diameter of 3.4 mu m with a coefficient of variation of particle size distribution of 4.0%