The electrochemical behavior of an all solid-state Li/Li x MnO2 polymer cell was evaluated by using three kinds of polymer-electrolytes in the composite positive electrodes. The discharge-rate capability and cycle life was significantly improved by using low-molecular weight polymer-electrolyte. It was confirmed that the improvement is due to the smaller charge transfer resistance between a polymer-electrolyte/cathode material interface, and the compatibility of polymer-electrolyte toward the cathode material is much more direct than the ionic conductivity of the polymer-electrolyte in the effects on its rate capability and cyclability.