Both high ionic conductivity and excellent mechanical properties are required to solid polymer electrolytes (SPEs) for all-solid lithium polymer batteries. We synthesized a solid polymer electrolyte with micro phase separation structure and its electrochemical characteristics were investigated. The highest value of ionic conductivity was obtained at a concentration of 5 mol% of lithium salt to ethyleneoxide unit ([EO]). The ionic conductivity of this SPE was 2 x 10(-4) S cm(-1) at 30 degrees C. An all-solid state lithium polymer battery, Li/SPE/Li CoO2 composite cathode cell, exhibited an excellent charge/discharge character with keeping a discharge capacity of 100 mAh g(-1) after 100 cycles at room temperature. This SPE was electrochemically stable and did not decompose up to 4.5 V. (c) 2005 Elsevier B.V. All rights reserved.