All-solid-state In/LiMn2O4 cells with the 80Li(2)S center dot 20P(2)S(5) (mol %) solid electrolyte were assembled. Cycle and rate performances were evaluated. The cell showed the first discharge capacity of 55 mAh g(-1) at a current density of 0.064 mA cm(-2) and retained the reversible capacity of 47 mAh g(-1) after 100 cycles. The capacity decreased with increase in the current density, and the overpotential at the beginning of discharge was observed. The discharge capacity was about 23 mAh g(-1) at a current density of 2.6 mA cm(-2). To identify the cause of the overpotential, impedance measurements were carried out, and resistance components were analyzed by changing the state of charge and by evaluating an all-solid-state Li1-xMn2O4 symmetric cell. The interfacial resistance between the LiMn2O4 electrode and the solid electrolyte was identified after the charge process. The transmission electron microscopy observation and energy-dispersive X-ray analysis, showed that Mn slightly diffused from LiMn2O4 to the solid electrolyte at the interface.