Solid-state electrolytes such as lithium ion conducting ceramic or solid polymers have been studied as substitutes for liquid electrolytes, but critical problems exist at the interfacial resistance between the solid electrode and the solid electrolyte. In this study, we combined 80 wt % Li1.3Ti1.7Al0.3(PO4)3 (LTAP) as a lithium ion conducting ceramic with 10 wt % of poly(vinylidene fluoride) (PVdF) as a binder, and 10 wt % 1 M LiPF6 in ethyl carbonate/dimethyl carbonate (EC/DMC) to develop a new composite electrolyte. The ceramic-based composite electrolyte showed thermal stability and high ionic conductivity through reduction of the interface resistance. The lithium ion conductivity of the composite electrolyte was 8.9×10−4 S cm−1 at room temperature without leakage. Electrochemical tests of the Li1+xMn2O4–LTAP-based composite electrolyte–Li1−xMn2O4 cell showed that the composite could be utilized as a potential electrolyte for high-safety lithium-ion batteries.