Polyimide/silica (PI/SiO2) hybrid nanocomposites were prepared by the sol-gel process directly from a soluble polyimide. This soluble PI was synthesized from a diamine with a pendant phenyl hydroxyl group, 4,4'-diamino-4"-hydroxy triphenyl methane (DHTM) and a dianhydride, pyromellitic dianhydride (PMDA), followed by cyclodehydration. Three ways of preparing PI/SiO2 hybrid nanocomposites were investigated in this study. Two of them used the coupling agent 3-glycidyloxy propyl trimethoxysilane (GPTMOS) to enhance the compatibility between PI and silica. The coupling agent can react with the PI to form covalent bonds. The structures of the modified hybrid nano-composites were identified with a FTIR, whereas the size of the silica in polyimides was characterized with a scanning electron microscope. The size of silica particles in the modified system was <100 nm. The covalently bonded PI/SiO2 hybrid nanocomposites prepared by the novel third approach exhibited good transparency when the silica content was <15%. Moreover, their thermal and mechanical properties exhibited a significant improvement. (C) 2004 Wiley Periodicals, Inc.