The influence of various halide additives milled with magnesium hydride (MgH2) on its decomposition temperature was studied. The optimum amount of halide additive and milling conditions were evaluated. The MgH2 decomposition temperature and energy of activation reduction were measured by temperature programmed desorption (TPD) and differential scanning calorimetry (DSC). The difference in catalytic efficiency between chlorides and fluorides of the various metals studied is presented. The effects of oxidation state, valence and position in the periodic table for selected halides on MgH2 decomposition temperature were also studied. The best catalysts, from the halides studied, for magnesium hydride decomposition were ZrF4, TaF5, NbF5, VCl3 and TiCl3 Crown Copyright (C) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.