The hydrogen storage properties of a novel Mg2Ni alloy powder prepared with a mechanical grinding method were investigated, This alloy powder was transformed to an amorphous-like state by this treatment. As a result, an electrode of this alloy shows a large discharge capacity (750 mAh/g) which is 2.5 times higher than that of AB(5)-type alloys. This significant improvement of hydrogen storage properties seems to be achieved by the increase in the crystal boundary and a heterogeneous strain in this alloy. The hydrogen equilibrium pressure of this alloy increased markedly.