The transparent and flexible solid polymer electrolytes (SPEs) are fabricated from polyacrylonitrile-polyethylene oxide (PAN-PEO) copolymer. The formation of the copolymer is confirmed by Fourier-transform infrared spectroscopy (FTIR) and Gel permeation chromatography (GPC) measurements. The effects of acrylonitrile (AN) wt% content and M-n(PEO) on ionic conductivity are investigated by alternating current (ac) impedance spectroscopy. By controlling and adjusting the AN wt% content and doping PEO with high molecular weight, the ionic conductivity of SPEs is optimized. The ionic conductivity of PAN-PEO solid polymer electrolytes is found to be high 6.79 x 10(-4) S cm(-1) at 25 degreesC with an [EO]/[Li] ratio of about 10, and are electrochemically stable up to about 4.8 V versus Li/Li+. The conductivity and interfacial resistance remain almost constant even at 80 degreesC.