The La0.5Ni1.5Mg17 alloy prepared by hydriding combustion synthesis (HCS) was investigated by an isovolumetric method and X-ray diffraction and this alloy has a large hydrogen storage capacity with good hydriding/dehydriding (H/D) kinetics. The kinetics of hydrogen absorption/desorption (A/D) in the two-phase (alpha-beta) region has been studied between 523 and 573 K under approximately isobaric conditions and the experimental data were analyzed to find the kinetics mechanisms for both the H/D processes. It is shown that the rate-controlling step of the H/D processes is the diffusion of hydrogen, due to the good agreement between the experimental results and calculated curves using a simple new kinetic model. The activation energies are calculated to be 86.8 kJ/mol H-2 for absorption and 84.9 kJ/mol H-2 for desorption, which were much smaller than that of MgH2, and can be attributed to the La and Ni additions. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.