The mini-emulsification and mini—emulsion polymerization of methyl methacrylate(MMA)／nanosilica dispersion were investigated．The rnimi-emulsification was carried out by ultrasonic treatment．It was found that more than 90％ silica particles would be escaped from submicren MMA droplets to water phase after ultrasonic treatment when MMA/unmedified silica dispersion was used．Almost all silica particles stably stayed in MMA droplets when silica particles were treated by 3-(trimethoxysilyl)propyl methacrylate(MPS)coupling agent at 40℃ for 24 h before being dispersed in aqueous phase．This was caused by the effective grafting of MPS onto silica particles．and the decrease of hydrophilicity of silica particles．Poly(methyl methacrylate)／nanosilica composite latex particles were prepared by mini—emulsion polymerization of silica-containing MMA using sodium lauryl sulfate(SDS)as the surfactant and hexadecane(HD) as the costabilizer．The composite latex particles were dispersed stably

the surfaces of composite latex were sleek and the silica particles could hardly be found in the water phase．It was considered that the silica particles had been encapsulated in the composite particles．