Element substitution is an effective strategy for improving Mg-based alloys in their hydrogenation/dehydrogenation property. Thereby, in this paper, Sm was selected to partially replace La in a La-Mg-based alloy for improving its hydriding and dehydriding performance. The alloys with the compositions of Mg80Ni10La10-xSmx (x = 0-4) were manufactured through vacuum induction melting. Their microstructures and phase compositions were measured by XRD, SEM and HRTEM. The isothermal hydrogen storage property was tested through an automatic Sieverts apparatus. Non-isothermal hydrogen desorption performance was measured through TGA and DSC. Arrhenius and Kissinger methods were adopted to calculate the dehydrogenation activation energy of alloys. The results reveal that all of the experimental alloys can reversibly absorb and release a large amount of H-2 at appropriate temperatures. The substitution of Sm for La ameliorates the hydriding and dehydriding kinetics, but it results in an undesired reduction of hydrogen absorption and desorption capacities. Substituting La by Sm decreases the initial hydrogen release temperature of the hydride visibly. Furthermore, substituting Sm for La engenders the dehydrogenation activation energy decline clearly, which is considered as the main reason for the improved hydrogen desorption kinetics resulted from Sm replacing La. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.