New types of solvent-free, lithium-conducting polymer electrolytes have been prepared by hot-pressing a blend of poly(ethylene oxide) (PEO) and a lithium bis(oxalato)borate, LiBC4O8 (LiBOB) salt. The membranes have been characterized in terms of ionic conductivity and lithium ion transference number. In addition, the thermal and the structural properties were investigated by differential scanning calorimetry and X-ray diffraction. The results show that the PEO-LiBOB membranes have a high ionic conductivity even at low-medium temperatures. (C) 2004 The Electrochemical Society.