Complexes of poly(ethylene oxide)-grafted poly(methylmethacrylate) (PEO-PMMA) and lithium (Li) salts have been prepared as polymeric solid electrolytes for rechargeable Li batteries. As high conductivities as 10(-3) S cm(-1) at room temperature were obtained for the PEO-PMMA-based electrolytes containing Li salts with a liquid plasticizer. Effects of the crown ethers in the electrolytes were examined on the ionic conductance behavior. The addition of 12-crown-4 (12Cr4) or 15-crown-5 (15Cr5) improved the ionic conductivity to a small extent. However, the ionic mobility of Li+ in the electrolyte was improved by the addition of 15Cr5. The transport number of Li+ in the electrolytes containing 15Cr5 was much higher than those in the electrolytes without crown ethers. The specific solvation of Li+-15Cr5 contributes not only to the improvement in the ionic mobility of Li+ but also to the suppression in the reaction rate of the Li electrode in the polymeric electrolytes.