Abstract The Mg–10.6 wt. % La–3.5 wt. % Ni nanoparticles are prepared by hydrogen plasma-metal reaction method. These nanoparticles are made of Mg, LaH3 and a small amount of Mg2Ni. The as-prepared Mg nanoparticles of 180 nm are single crystalline and quasi-spherical in shape, and they change into polycrystalline after activation. LaH3 and Mg2Ni nanoparticles are nearly spherical in shape with the mean particle size of 15 nm, and disperse on the surface of Mg. The Mg–10.6La–3.5Ni nanoparticles can absorb 3.2 wt. % H2 in less than 15 min at 523 K and accomplish a high hydrogen storage capacity of 6.5 wt. % H2 in less than 10 min at 673 K, almost reaching the theoretical gravimetric capacity. They can release 4.2 wt. % H2 in 3 min at 623 K. The synergistic catalytic effect of LaH3 and Mg2Ni nanoparticles, the nanostructure and the low oxide content of Mg nanoparticles promote the hydrogen sorption process with the low hydrogen absorption activation energy of 39.1 kJ mol−1.