Highly conductive polymer electrolytes supported by a microporous separator were prepared and characterized. These polymer electrolytes were prepared by coating poly(ethylene oxide) (PEO) and poly(ethylene glycol dimethacrylate) (PEGDMA) onto a microporous polyethylene membrane, and soaking them in an electrolyte solution. The relative weight ratio of PEO and PEGDMA coated on the microporous membrane proved to play a critical role in determining uptake of an electrolyte solution and ionic conductivity. The electrolyte optimized in this work displayed a high ionic conductivity and electrochemical stability, exhibiting no solvent leakage. An encapsulation of electrolyte solution within the porous membrane diminished the passivation of lithium electrodes. With these electrolytes, lithium-ion polymer cells composed of a carbon anode and LiCoO2 cathode were assembled, and their electrochemical performances were evaluated.