The catalytic mechanism of Nb2O5 and NbF5 on the dehydriding property of Mg95Ni5 prepared by hydriding combustion synthesis and mechanical milling (HCS+MM) was studied. It was shown that NbF5 was more efficient than Nb2O5 in improving the dehydriding property. In particular, the dehydriding temperature onset decreases from 460 K for Mg95Ni5 to 450 K for Mg95Ni5 with 2.0 at.% Nb2O5, whereas it decreases to 410 K for that with 2.0 at.% NbF5. By means of X-ray diffraction and X-ray photcelectron spectroscopy, it was confirmed that the interaction between the Nb ions and the H atoms and that between the anions (O2- or F-) and Mg2+ existed in Mg95Ni5 doped with Nb2O5 or NbF5. Further, the pressure-concentration-isotherms analysis clarified that these interactions destabilized the Mg-H bonding, and that NbF5 had a better effect on the destabilization of the Mg-H bonding than Nb2O5 contributing to the better dehydriding property Of (Mg95Ni5)2.0-NbF5. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.