The hydriding properties of Mg-xNi (x = 13.5, 23.5 and 33.5 wt%) alloys with different microstructures produced by various processing routes were evaluated in this study. The hydrogen storage capacity and kinetics of hydriding of Mg-xNi alloys were strongly dependent on their microstructures. The capacity and kinetics of hydriding were larger and faster when the average size of the hydriding phase was smaller and the volume fraction of the phase boundary was larger. (c) 2006 Elsevier B.V. All rights reserved.