Solid polymer electrolytes with high ionic conductivities, good mechanical properties, dimensional stability, and easy processability were obtained from poly(ethylene oxide)-block-polyethylene (PEO-b-PE)-loaded poly(ethylene oxide) (PEO)/lithium perchlorate (LiClO4). In this article, we reported that the ionic conductivity and mechanical properties were remarkably increased due to the addition of the PEO-b-PE compared to that of PEO/LiClO4 electrolyte. Scanning electron microscope (SEM), optical micrograph, and X-ray diffraction (XRD) results indicate that the addition of the copolymer, PEO-b-PE, decreased the defects of the PEO electrolyte films. Good dimensional stability was observed by dynamic rheological techniques up to 100 degrees C (higher than the melting point of PEO, 65 degrees C). A bicontinuous phase structure, that is crystalline PE domains within a matrix of PEO/salt, was proposed as the mechanism for such comprehensive enhancements in the ionic conductivity, mechanical properties, and dimensional stability obtained simultaneously in this study through a facile approach based on incorporation of a copolymer.