Polymer modification of monodispersed colloidal silica (0.5 μm) and introduction of carboxyl groups on the surface are studied. The reactions of surface silanol with alternate copolymer silane coupling agents, prepared by maleic anhydride and styrene, methyl methacrylate or vinyl acetate, are effectively promoted by azeotropic removal of ethanol and water from the reaction system. Cross-linking of bound polymer on silica particles by esterification with diol results in simultaneous formation of carboxyl group of 0.15-0.21 mmol/g. The surface carboxyl groups are able to bind poly(methyl methacrylate) chains (Mn, 1700) of 0.86-1.29 mg/g by condensation reactions.