In the present study, poly(ethylene oxide) (PEO) and poly(vinylidene fluoride) (PVDF) blend based composite polymer electrolytes (CPEs) had been prepared by using a different content of nano-sized BaTiO3 filler, in order to examine the filler addition effect on the structural modification and electrochemical properties. The crystallinity and thermal stability of the CPEs was evaluated using differential scanning calorimeter (DSC), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The electrochemical properties of CPEs were measured by the AC impedance method and cyclic voltammetry (CV). As a result, Both DSC and XRD results indicated that the CPE showed reduced crystallinity after the introduction of BaTiO3 filler. From the ionic conductivity results, the CPE containing BaTiO3 filler 15 wt.% showed the highest ionic conductivity (1.2 x 10(-4) S/cm) with a wide electrochemical stability window and an excellent thermal stability at room temperature. This indicated that electrochemical characteristics are dependent on the reduced crystallinity by the addition of nano-sized BaTiO3 filler content. (C) 2013 Elsevier B.V. All rights reserved.