The amorphous alloys of Mg-Ni-Zr were synthesized by mechanical alloying process, in which the effects of Zr addition were studied. A small shift of the broadening amorphous peak due to Zr additions was observed. The equilibrium hydriding pressure increased continuously with hydrogen contents in the amorphous alloys, while there was an obvious plateau pressure of 10(-4) MPa in the crystalline Mg2Ni phase. The Zr addition lowered the equilibrium hydriding pressure and increased the hydrogen solubility from 1.4 wt% for Mg-Ni to 2.2 wt% for Mg-Ni-Zr. Accompanied by amorphization, the hydrogen discharge capacity increased largely, and reached 580 mA h/g for Mg-Ni-Zr alloy. The chronopotentiometric experiments were performed to investigate the hydrogen diffusion in the alloy powder in the high over-potential range. The diffusivity of hydrogen in the Zr-contained alloy was lower than the Mg-Ni binary amorphous alloy or in Mg2Ni nanocrystalline alloy. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.