Nanocomposites of lithium ion conductors (Li2SiO3 and Li1.3Al0.3Ti1.7(PO4)(3)) and electrode materials (TiO2, Li0.01TiO2 and FePO4) were prepared to investigate interfacial structure and ionic conductivity at the interface between solid electrolytes and electrode materials. It was revealed that lithium ions in the solid electrolytes were attracted to the cathode materials with increasing electrode potential, which increases lithium vacancies in solid electrolytes. For the FePO4 containing composites, due to the high electrode potential, lithium transfer across the interface and ionic conduction through the cathode materials was remarkable. The results suggest that severe lithium depletion occurs and interfacial resistance is large at the interface of high ionic conductors and cathode materials.