The effect of Ni-substitution on the structure and hydrogen storage properties of Mg2Cu1-xNix (x = 0, 0.2, 0.4, 0.6, 0.8, 1) alloys prepared by a method combining electric resistance melting with isothermal evaporation casting process (IECP) has been studied. The X-ray single-crystal diffraction analysis results showed that the cell volume decreases with increasing Ni concentration, and crystal structure transforms Mg2Cu with face-centered orthorhombic into Ni-containing alloys with hexagonal structure. The Ni-substitution effects on the hydriding reaction indicated that absorption kinetics and hydrogen storage capacity increase in proportion to the concentration of the substitutional Ni. The activated Mg2Cu and Mg2Ni alloys absorbed 2.54 and 3.58 wt% H, respectively, at 573 K under 50 bar H-2. After a combined high temperature and pressure activation cycle, the charged samples were composed of MgH2, MgCu2 and Mg2NiH4 while the discharged samples contained ternary alloys of Mg-Cu-Ni system with the helpful effect of rising the desorption plateau pressures compared with binary Mg-Cu and Mg-Ni alloys. With increasing nickel content, the effect of Ni is actually effective in MgH2 and Mg2NiH4 destabilization, leading to a decrease of the desorption temperature of these two phases. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.