La2Mg17-based nanocrystalline alloys were prepared by ballmilling La2Mg17 alloy with Ni powders. Electrochemical charging and discharging of the ballmilled La2Mg17-based nanocrystalline alloy succeeded due to the formation of highly dispersed metallic Ni particles through the nanocrystalline alloy matrix. The first discharge capacity of the La2Mg17 alloys ballmilled with Ni powders in a weight ratio of 1:2 was near 990 mAh/g, corresponding to a hydrogen storage capacity of 3.69 wt %. Inlaid metallic Ni at the surface layer of the nanocrystalline alloy matrix served as electrocatalytic reaction sites and hydrogen adsorption sites to accelerate the electrochemical charging and discharging process. (C) 2004 The Electrochemical Society.