In this study, TiO2 sols with very small particle sizes (~5 nm) were synthesized in an aprotic solvent, N,N-dimethylacetamide (DMAc) and N,N- dimethylformamide (DMF), via sol-gel reaction at room temperature. The TiO2 sol showed long-term storage stability (30 days) and can provide operating control for the preparation of high–refractive–index polyimide-TiO2 hybrid thin films. By means of spin coating and multistep baking (up to 300 oC), the hybrid thin films were prepared from the solutions composed of soluble polyimide and TiO2 sol. The FE-SEM images showed a smooth and uniform morphology of the hybrid thin films. TiO2 domains were in the nanometer range, thus avoiding the light scattering. The refractive indices at 633 nm of the prepared hybrid thin films increase from 1.63 to 2.16 with increasing TiO2 content, which suggested the potential application to anti-reflective coatings and optical waveguides.