A series of Polyimide/TiO2 (PI/TiO2) nano-composites were successfully prepared by incorporating different nano-sized TiO2 contents into PI which derived from pyromellitic dianhydride (PMDA) and a flexible diamine 4,4-bis(3-aminophenoxy)biphenyl (4,3-BAPOBP) via in-situ polymerization and a thermal imidization method. The micromorphology, chemical structure of samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR). The SEM results show that when the content of nano-TiO2 is lower, the nano-TiO2 can be distributed uniformly in the matrix by the method of this experiment scheme, and signs of agglomeration have begun to appear when the TiO2 content is 12 wt.%. XRD patterns reveal the crystal structure of TiO2 remains unchanged and stable after being doped into PI matrix, and the TiO2 nano-particles have good compatibility with PI matrix