Electrochemical characterization of Mg2Ni alloy was carried out at various temperatures. Discharge capacity of the Mg2Ni alloy electrode remarkably increased at 70 degrees C and 90 degrees C in comparison with that at 30 degrees C. The charge-discharge curves as well as the measured pressure-composition isotherms revealed that most of all hydrogen absorbed by charging were reversibly desorbed in discharging at 70 degrees C and 90 degrees C.