Microstructural characteristics and electrochemical properties of Mg40Al60 hydrogen storage alloy prepared by mechanical alloying (MA) method were studied by XRD, discharge capacities, polarization curves and electrochemical impedance spectroscopies(EIS). The intensities of XRD peaks become weak and XRD peaks have a broadening with the increment of ball milling time due to fine grain size and increased internal stress. The discharge capacities of the alloy increase before the alloyed powders were milled for 10h, but they decrease after the alloyed powders were milled for 10h with the increment of ball milling time. The discharge capacities are highest when the alloyed powders were milled for 10h. There are passive phenomena in polarization curves. The corrosion current densities increase with time at the beginning of ball milling and then decrease. The electrochemical impedance spectroscopies(EIS) are composed of a single capacitive loop and the electrode reaction is controlled by charge transfer at alloy/electrolyte interface.