Recently, it was shown that hydrogen absorption-desorption kinetics in magnesium were improved by milling magnesium hydride (MgH2) with transition metal oxides. Herein, we investigate the role of the most effective of these oxides, Nb2O5 when added in larger volume fraction. The effect of Nb2O5 on magnesium crystalline structure, particle size and (ab)desorption properties has been characterised. Moreover, we report that pure MgH2 can also show fast hydrogen sorption kinetics after a long milling time. The effects of Nb2O5 on MgH2 sorption properties are rationalised in a new approach considering Nb2O5 as a dispersing agent, which helps reduce MgH2 particle size during milling. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.