A series of polyimide (PI)/silica hybrid films were prepared by sol-gel method, using hydrolyzed tetraethoxysilane and poly amic acid-imides (PAA-Is), which were different imidization degree controlled by chemical imidization method. The imidization degree was characterized by Fourier transform infrared spectra and their corresponding morphology was characterized by scanning electron microscopy. The results show that there are two kinds of silica particles and their formative morphology obeys the double phase separation mechanism. According to the increase of PAA-I imidization degree, amount of nano silica particles decreased and the diameter of macro silica particles increased in the hybrid films. Tensile testing, dynamic mechanical analysis, and thermal mechanical analysis results show that, according to the amount of nano silica particles increasing, the hybrids have the higher the mechanical properties, glass transition temperature (T-g), and thermal expansion coefficient. Through controlling PI/silica hybrid films microstructure, its mechanical properties can be controlled. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2772-2777, 2010