O 3 contents into PI which derived from pyromellitic dianhydride (PMDA) and a flexible diamine 4,4-bis(3-aminophenoxy)biphenyl (4,3-BAPOBP). The micromorphology, chemical structure, dielectric, mechanical properties and glass transition temperatures (T g) of prepared films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), LCR metry, electronic tensile testing and differential scanning calorimetry (DSC). SEM images show uniform distribution of Al 2 O 3 nanoparticles in matrix. FTIR spectra indicate that Al 2 O 3 nanoparticles are functionalized with γ-aminopropyl triethoxysilane (γ-APS) and the imidization was complete. XRD patterns reveal the peaks of PI/Al 2 O 3 composite films were similar to those of Al 2 O 3 , indicating that the crystal structure of Al 2 O 3 remains unchanged and stable after being doped into PI matrix. Meanwhile, the effects of additives on the dielectric and mechanical properties of composite films were also studied. The results show the dielectric constant and dielectric loss of hybrid materials increase with the addition of Al 2 O 3 nanoparticles. The electrical breakdown strength and tensile strength of PI/Al 2 O 3 can be markedly improved by the addition of appropriate amounts of Al 2 O 3 to the PI matrix.