Poly(methyl methacrylate) (PMMA)/Titanium oxide (TiO2) composite particles were prepared via in-sitn emulsion polymerization of MMA in the presence of TiO2 particles. Before polymerization, the TiO2 particles was modified by the silane coupling agent, which is crucial to ensure that PMMA reacts with TiO2 via covalent bond bindings. The structure of the obtained PMMA/TiO2 composite particles was characterized using Fourier transform infrared spectra (FTIR) and thermogravimetric analysis (TGA). The results indicate that there are covalent bond bindings between PMMA macromolecules and TiO2 particles. Based on these facts, several factors affecting the resulting PMMA/ TiO2 composite system, such as the type of coupling agents, the mass ratio of the MMA to the modified TiO2, the emulsifier concentration, and the initiator concentration, etc., were examined by the measurement of conversion of monomers, the gel content of polymers, the percentage of grafting, and the grafting efficiency, using gravity method or TGA method. As a result, the optimized recipe was achieved, and the percentage of grafting and the grafting efficiency could reach 216.86 and 96.64%, respectively. In addition, the obtained PMMA/TiO2 composite particles were found to a stable colloidal dispersion in good solvent for PMMA. (c) 2006 Wiley Periodicals, Inc.