Continuous emulsion copolymerizations of styrene(St) and methyl methacrylate(MMA) were carried out at 50degreesC in a single continuous stirred tank reactor (CSTR) using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator, respectively. The effect of operational variables such as the initiator and emulsifier concentrations in the feed and the mean residence time on the kinetic behavior was examined with the weight ratio of SUMMA in the monomer feed fixed at 1.0. It was found that 1) oscillation in monomer conversion takes place, although its amplitude is comparatively small compared with that usually observed in the continuous emulsion polymerization of vinyl acetate in a CSTR, 2) the (time-average) steady-state total monomer conversion is proportional to the 1.7 power of the emulsifier, to the -0.2 power of the initiator concentrations and to the 1.0 power of the mean residence time, and 3) the (time-average) steady-state number of polymer particles produced is proportional to the 2.5 power of the emulsifier concentration, to the -0.4 power of the initiator concentration and to the -0.7 power of the mean residence time.