The effect of partial substitution on the hydrogen storage properties of Mg2Ni was investigated. It was found that as a result of substitution of Mg with a more electronegative element (Al or Mn), absorption of hydrogen easily occurs at lower temperature. The alloy powder prepared with a mechanical grinding method was also studied. This alloy powder was found to be mainly changed to an amorphous-like state by this treatment. Consequently, the negative electrode of the mechanically ground Mg2Ni alloy shows a large discharge capacity, 750 mAh/g, which is two and one-half times that of AB(5) type alloys. It was also found that the hydrogen reversibility of the mechanically ground Mg(1.0)A(0.1)Ni alloy electrode remarkably increased.