Poly(styrene-methylmethacrylate), poly(styrene-methylacrylate) and poly(styrene-2-hydroxyethylmethacrylate) were prepared by the semi-continuous soap-free emulsion polymerization method. In these syntheses, the feeding time of more hydrophobic monomer, i.e., styrene was 2 hours. The stability of latices determined by the sedimentation rate method was high. Average molecular weights of sample latices were 10⁵-10⁶ order, and molecular weight distributions of copolymer latices were comparatively narrow. Particle size of dried latex determined by SEM was larger than that of batch type polymer. Kinetics of semi-continuous soap-free emulsion polymerization was investigated in the synthesis of poly(styrene-methylmethacrylate) latex. In semi-continuous system generally, the initial rate of polymerization was low, but entire kinetics was similar to that of general emulsion polymerization. Total activation energy was 17.13 kcal. mol^-1.