The grafting of polystyrene onto a nanometer silica surface by microemulsion polymerization is described. Silica was functionalized with 3-methacryloxypropyltrimethoxysilane coupling agent before polymerization. A mixture of ionic and non-ionic surfactants as well as water-soluble and oil-soluble initiators were used. The effect of the amount of silica and ionic surfactant on the graft polymerization was studied. The graft polymerization procedure for styrene was also applied to methyl methacrylate. Composite particles with a core-shell structure were obtained and the yield and grafting efficiency of monomer were high.