Hydrogen storage materials research is entered to a new and exciting period with the advance of the nanocrystalline alloys, which show substantially enhanced absorption/desorption kinetics, even at room temperatures. In this work, hydrogen storage capacities and the electrochemical discharge capacities of the Mg-2(Ni, Cu)-, LaNis-, ZrV2-type nanocrystalline alloys and Mg2Ni/LaNi5-, Mg2Ni/ZrV2-type nanocomposites have been measured. The electronic properties of the Mg2Ni1-xCux, LaNis and ZrV2 alloys were calculated. The nanocomposite structure reduced hydriding temperature and enhanced hydrogen storage capacity of Mg-based materials. The nanocomposites (Mg,Mn)(2)Ni (50 wt %)-La(Ni,Mn,Al,Co)(5) (50 wt%) and (Mg,Mn)(2)Ni (75 wt%)-(Zr,Ti)(V,Cr,Ni)(2.4) (25 wt%) materials releases 1.65 wt% and 1.38 wt% hydrogen at 25 degrees C, respectively. The strong modifications of the electronic structure of the nanocrystalline alloys could significantly influence hydrogenation properties of Mg-based nanocomposities. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.