Mg (200 nm) and LaNi5 (25 nm) nanoparticles were produced by the hydrogen plasma-metal reaction (HPMR) method, respectively. Mg-5 wt.% LaNi5 nanocomposite was prepared by mixing these nanoparticles ultrasonically. During the hydrogenation/dehydrogenation cycle, Mg-LaNi5 transformed into Mg-Mg2Ni-LaH3 nanocomposite. Mg particles broke into smaller particles of about 80 nm due to the formation of Mg2Ni. The nanocomposite showed superior hydrogen sorption kinetics. It could absorb 3.5 wt.% H-2 in less than 5 min at 473 K, and the storage capacity was as high as 6.7 wt.% at 673 K. The nanocomposite could release 5.8 wt.% H-2 in less than 10 min at 623 K and 3.0 wt.% H-2 in 16 min at 573 K. The apparent activation energy for hydrogenation was calculated to be 26.3 kJ mol(-1). The high sorption kinetics was explained by the nanostructure, catalysis of Mg2Ni and LaH3 nanoparticles, and the size reduction effect of Mg2Ni formation. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.