We have fabricated the materials composed of the Mg and the Ni nanoparticles and clarified the hydrogen storage property by using TEM, XPS and QCM. The Mg and the Ni nanoparticles have been fabricated by gas evaporation method and been mixed. The diameters of the Mg and the Ni nanoparticles have been estimated as 20.0 +/- 8.4 and 4.7 +/- 2.0 nm, respectively. And the Mg and the Ni nanoparticles as prepared sample possess almost clean surface. This sample can absorb the hydrogen under atmospheric pressure at 30 degrees C before completely oxidized. However, the hydrogen storage ability of this sample has been lost by the adsorption of residual gases even under vacuum condition in several hours after the end of fabrication. Due to the Mg oxide shell on the surface of the Mg nanoparticles is formed by the residual gases, the hydrogenation of the Mg nanoparticles are hindered. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.