The rate-controlling steps for the hydriding reaction of a mechanically alloyed mixture Mg-10 wt% Ni were determined by comparing empirical results with theoretical rate equations established earlier. For its hydriding reaction at 575-615 K and 5.4-16.1 bar H-2, the rate-control ling steps are the bulk and Knudsen flow through the pores, cracks and interparticle channels, and the diffusion of hydrogen atoms through the growing hydride layer, varying with the reacted ranges. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.