Novel nanocomposite films of TiO2 nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol-A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent-resistance, good thermal stability, and mechanical properties were prepared by incorporating surface-modified TiO2 nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO2 nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long-chain alkyl amines. These TiO2 nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free-standing films were obtained by drying a mixture of TiO2 nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO2 nanoparticles of 3-6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO2 nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films; of TiO2 and poly(bisphenol-A and epichlorohydrin) was in the range of 1.58-1.81 at 589 nm, which linearly increased with the content of TiO2 nanoparticles from 0 to 80 wt %. (c) 2007 Wiley Periodicals, Inc.