Polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from a mixture of tetraethoxysilane (TEOS), a solution ofpolyamic acid in N, N-dimethylacetamide and water of pH 7 and pH 3. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the polyamic acid solution, followed by heating at 270°C. Fairly flexible films were obtained for silica contents up to 70 wt%. The films containing less than 8 wt% of silica were yellow and transparent, whereas the films with higher silica contents were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 and 1.69 g/cm3 (pH 7 and pH 3). The29Si nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with submicron diameter were observed in the hybrid films containing less than 8 wt% silica, whereas larger particle size around 5 μ m in the case of higher silica content. The decomposition temperature of the hybrid films increased with increasing silica content. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. Tensile properties, such as elongation at break, tensile strength, and tensile modulus also exhibited the same tendency. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3 × 10−5 and 0.3 × 10−5 (pH 7 and pH 3), which suggested that the silica had a porous structure.