The hydrogen storage property of the binary nanoparticles composed of Mg and Pd has been investigated by the QCM technique without the exposure to the air. The two types of nanopardcles have been fabricated by the gas evaporation method with the He gas. The one is the nanoparticles composed of the both Mg and Pd atoms (Mg-Pd NPs) and the other one is the composite of the Mg and Pd nanoparticles (Mg NPs-Pd NPs). Both the Mg-Pd NPs and the Mg NPs-Pd NPs can absorb the hydrogen under the room temperature and 1 atm of H-2 gas. However, the desorptions of the hydrogen have not been observed about the both samples. We have also studied the chemical state of the NPs by XPS and XAFS. The XAFS analyses have revealed that the MgH2 in the NPs can not be dehydrogenated at the room temperature even if the catalytic effect of the Pd. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.