Unfavourable stability and sluggish de/re-hydrogenation kinetics hamper the application of MgH2 as a hydrogen storage material for mobile fuel cell systems. In the present work, it can be destabilized effectively by LiAlH4 in as-synthesized MgH2-LiAlH4 composites (1:1,21 and 4:1 in mole ratio). The onset dehydrogenation temperature of MgH2 is observed at around 250 degrees C, which is over 50 degrees C lower from that of as-milled MgH2. Differential scanning calorimetry (DSC) measurements indicate that the enthalpies of MgH2-relevant decomposition in MgH2-LiAlH4 composites (1:1, 2:1 and 4:1 in mole ratio) are 45, 48.6 and 61 kJ mol(-1) H-2, respectively. These values decrease significantly from that of as-milled pristine MgH2 (76 kJ mol(-1) H-2), demonstrating the destabilization of MgH2 in this system. The destabilization mechanism is investigated by X-ray diffraction (XRD) analyses. It was found that the whole dehydrogenation process can be divided into two stages: the first stage is the two-step decomposition of LiAlH4 and during the second stage, the yielded LiH and Al phases decompose MgH2 to form Li0.92Mg4.(08) and Mg17Al12 phases, respectively. The mutual destabilization between MgH2 and LiH was first observed in this study. Moreover, the reaction is fully reversible. The isothermal kinetics shows that the doped LiAlH4 is beneficial to the enhancement of the dehydrogenation kinetics of MgH2. (C) 2008 Elsevier B.V. All rights reserved.