Polymeric solid electrolytes have great advantages over liquid electrolytes in many respects such as high energy density, leak-proof, light weight, easy handling and wide range of operation temperature. This study was concentrated to research and develop solid polymer electrolyte(SPE) for Li secondary battery. We investigated the effects of lithium salt concentration, temperature dependence of conductivity and thermal stability of polyethylene oxide(PEO) electrolytes. The PEO electrolyte complexed with LiClO₄, at [EO]/[Li^+]ratio is 8, showed successful high conductivity(about 10^(-5)S/㎝) at 25℃ than other solvents.