Lithium fluoroalkylphosphate (LiPF3(CF3 CF2)(3)) based composite polymer electrolytes (CPE) have been prepared in the matrix of polyvinylidenefluoride-hexafluoropropylene (PVdF-HFP), using solvent casting technique. The membranes were gelled with ethylene carbonate and diethyl carbonate as a plasticizer and nanosized SiO2 and nanoporous Al2O3 as fillers. These membranes were subjected to a.c. impedance, DSC, SEM, FTIR, and Fluorescence studies. The a.c. impedance studies and activation energy calculation reveal that 2.5 wt % fillers containing membranes only exhibit maximum conductivity for SiO2 (1.16 mS cm(-1)) and Al2O3 (0-98 mS cm(-1)), compared to fillers free membranes and beyond 2.5 wt % of such fillers the conductivity tends to decrease. The enhancement of conductivity has been explained in terms of Vogel-Tamman-Fulcher (VTF) theory. Molecular interactions by FTIR and local viscosity environment by fluorescence studies have been investigated. (c) 2008 Wiley Periodicals, Inc.