In search of more viable solid polymer matrices for lithium ion conductors, solid solutions of LiClO4 in polyoxyethylene/polyethylenimine (PEO/PEI) (8:2, 5:5, and 2:8 by repeat units) blends were examined. In the 8:2 blends, conductivities increased with the decrease in the salt content. Conductivities in the 8:2- and the pure PEO systems were comparable at temperatures higher than 350 K. The drastic conductivity drop due to crystallization known for the PEO systems did not occur in the 8:2 systems; the 8:2 systems became ca. three orders of magnitude more conductive at room temperature. In contrast, the 5:5 systems suffered a severe conductivity drop near 330 K. The abrupt conductivity drop disappeared again in the 2:8 systems. They were more conductive than the pure PEI systems. Weak temperature dependence of conductivity made their room temperature condutivities even higher than those for the pure PEO systems.