Alumina (Al2O3) nanoparticles have been used as fillers in the preparation of poly(vinylidenefluoride-co-hexafluorpropylene) (P(VDF-HFP))-based porous polymer electrolyte. The degree of crystallization of polymer film filled with Al2O3 nanoparticles decreases with increase of the mass fraction of Al2O3 nanoparticles and the amorphous phases of polymer film expand accordingly. The Al2O3 nanoparticles play the role of solid plasticizer for polymer matrix. Nevertheless that excessive Al2O3 nanoparticles existing in polymer matrix leads to micro-phase separation between polymer matrix and fillers. As a result, both ionic conductivity and lithium ions transference number reduces whereas the activation energy for ions transport increases. When the polymer film is filled with 10% of the mass fraction of Al2O3 nanoparticles, polymer electrolyte possesses the ionic conductivity up to 1.95 × 10−3 Scm−1 and the lithium ions transference number to 0.73 while the activation energy for ions transport of them falls to 5.6kJmol−1. Effect of Al2O3 on the electrochemical properties of polymer electrolyte has been investigated in this paper. Analysis of FTIR spectra shows that there is the interaction between Al2O3 nanoparticles and polymer chains.