Various composite electrolytes (CE) were prepared by mixing polytetramethylene glycol-based waterborne polyurethane [WPU(PTMG)], polyethylene oxide (PEO), and LiClO4/propylene carbonate (PC). The conductivity of these CEs was investigated using ac impedance. Differential scanning calorimetry (DSC) and polarizing microscopy (PM) were employed for material characterization. The temperature dependence of the conductivity follows the Arrhenius law for samples with a LiClO4/PC content larger than 30%, while for samples with LiClO4/PC content approximating 8%, it shows linear segments separated by a transition zone between 25 and 65 degrees C. According to the ac and DSC results, the conductivity is increased, and the melting temperature is decreased by increasing the LiClO4/PC content. PM results indicate that the increase in PEO ratio increases the crystallinity of the PEO WPU(PTMG) films. When LiClO4/PC is added, the increase in PEO ratio results in an increase in conductivity. The CE comprising 33% PEG. 17% WPU(PTMG), and 50% LiClO4/PC exhibits conductivities as high as ca. similar to 10(-2) S cm(-1) at 85 degrees C and 5 x 10(-3) S cm(-1) at 15 degrees C.