A mechanical alloying process is introduced to produce nanocrystalline Mg2Ni-type metal hydride. The mechanical alloying process has recently emerged as a novel technique for producing alloy powders whose structures are nanocrystalline. Mg2Ni alloys were prepared using planetary ball mill starting from mixtures of elemental powders. Nanocrystalline Mg2Ni-type alloys were obtained by both the long-term ballmilling (mechanical alloying) and heat-treatment of the ballmilled powders. In comparison with the polycrystalline material, nanocrystalline Mg2Ni showed a lower temperature for hydrogenation and a higher discharge capacity at 30 degrees C. The partial substitution of Cu for Ni increased hydrogen absorption and desorption at 200 degrees C and greatly improved the discharge capacity of the nanostructured Mg2Ni electrode at 30 degrees C The discharge capacity of the 120 h milled Mg-2(Ni0.9Cu0.1) electrode was 350 mAh/g.