Single stage polymerizations proposed for producing micron-sized polymer particles in aqueous media by Konno et al, (Konno et al,, 1997; Konno and Orihara, 2000) are conducted to study the effect of agitation on particle size distribution. These polymerizations employed cationic and anionic surfactants or an amphoteric surfactant that were added to the system during reaction. Polymer yield and particle size distribution were measured in the polymerizations of styrene initiated with K2S2O8 in a reactor with different impellers in a range of impeller speed. Experimental results for the different impellers suggest that short mixing time is required for producing large particles with high monodispersity. It is shown that polymerization employing an amphoteric surfactant can produce micron-sized particles with higher monodispersity than polymerization employing cationic and anionic surfactants. In the former polymerization, Large particles with high monodispersity were formed at low impeller speed.