The transparent and flexible solid polymer electrolytes (SPEs) were fabricated from polyacrylonitrilepolyethylene oxide (PAN-PEO) copolymer which was synthesized by methacrylate-headed PEO macromonomer and acrylonitrile. The formation of copolymer is confirmed by Fourier-transform infrared spectroscopy (FTIR) measurements. The ionic conductivity was measured by alternating current (AC) impedance spectroscopy. Ionic conductivity of PAN-PEO-LiClO4 complexes was investigated with various salt concentration, temperatures and molecular weight of PEO (Mn). And the maximum ionic conductivity at room temperature was measured to be 3.54 X 10(-4) S/cm with an [Li+]/[EO] mole ratio of about 0.1. (c) 2006 Wiley Periodicals, Inc.