The synthesis of the hydrogen-storage alloy Mg2Ni has been carried out through a single-step mechanical alloying employing an energy ball mill. The synthesized ball-milled Mg2Ni alloy has been found to exist in the form of fine (nano) particles with sizes of about 40 Angstrom. The nanoparticle form has been found to lead to easy activation for hydrogenation by annealing at 300 degrees C (about 10(-4) Torr vacuum) for 30 min and hydrogen uptake has been found to commence from the first cycle itself.