Composite polymer electrolyte (CPE) films consisting of PEO, LiClO4, and Li1.3Al0.3Ti1.7(PO4)(3) with fixed EO/Li = 8 but different relative compositions of the two lithium salts were prepared by the solution casting method. The CPE films were characterized using SEM, DSC, electrical impedance spectroscopy (EIS), and ion transference number measurement. It was found that the incorporation of LiClO4 and Li1.3Al0.3Ti1.7(PO4)(3) into PEO by keeping EO/Li = 8 reduced the crystallinity of PEO from 50.34% to the range of 3.57-15.63% depending upon the relative composition of the two salts. The room temperature impedance spectra of the CPE films all exhibited a shape of depressed semicircle in the high frequency range and inclined line in the low frequency range, but the high temperature ones were mainly inclined lines. The Li+ ionic conductivity of the CPE films mildly increased and then decreased with increasing Li1.3Al0.3Ti1.7(PO4)(3) content, and the maximum conductivities were obtained at Li1.3Al0.3Ti1.7(PO4)(3) content of 15 wt % for all measuring temperatures, for example, 1.378 X 10(-3) S/cm at 100degreesC and 1.387 X 10(-5) S/cm at 25degreesC. The temperature dependence of the ionic conductivity of the CPE films follows the Vogel-Tamman-Fulcher (VTF) equation sigma = AT(-1/2) exp[-E-a/K-B(T - T-0)] The pseudo activation energies (E-a) were rather low, 0.053-0.062 eV, indicating an easy migration of Li+ in the amorphous phase dominant PEO. The pre-exponent constant A and ion transference number t(Li+) were found to have a similar variation tendency with increasing Li1.3Al0.3Ti1.7(PO4)(3) content and reached their maximums also at Li1.3Al0.3Ti1.7(PO4)(3) content of 15 wt %. (C) 2005 Wiley Periodicals, Inc.