To clarify the initial stage of particle formation in the emulsion polymerization of methyl methacrylate (MMA) using poly(vinyl alcohol) (PVA) as a protective colloid, a model experiment with a low concentration of MMA (1 ml/100 ml H 2O) was carried out in the presence of various initiators, ammonium persulfate (APS), 2,2′-azobis(2-amidinopropane)dihydrochloride (V-50) and 2,2′-azobis (isobutyronitrile) (AIBN). In the experiments using a large amount of PVA (1 g) at 70°C, the polymerization proceeded without any flocculation with all kinds of initiators, yielding stable emulsions with a diameter of approx. 90 nm and number of particles of 2×10 13/ml H 2O. The polymers in the emulsions were fractionated into three parts, acetone-soluble, water-soluble, and insoluble in both solvents. The amount of insoluble part was the largest in the APS system and the smallest in the AIBN system. The absence of the acetone-soluble part showed the high efficiency of grafting onto PVA in the initial stage of polymerization. In the experiments using a small amount of PBA (0.1 g) at 70°C, the emulsion polymerization occurred at a very early stage. With the increase in conversion, much coagulation took place due to the shortage of PVA. In this case, the ratio of PVA to monomer was 1:10, similar to the conventional emulsion polymerization of vinyl acetate (VAc). In the experiments without PVA, stable emulsions could not be obtained in all kinds of initiators. These results show the importance of the grafting in this emulsion system.