The present study compares the dehydrogenation kinetics of (2LiNH(2) + MgH(2)) and (LiNH(2) + LiH) systems and their vulnerabilities to the NH(3) emission problem. The (2LiNH(2) + MgH(2)) and (LiNH(2) + LiH) mixtures with different degrees of mechanical activation are investigated in order to evaluate the effect of mechanical activation on the dehydrogenation kinetics and NH(3) emission rate. The activation energy for dehydrogenation, the phase changes at different stages of dehydrogenation, and the level of NH(3) emission during the dehydrogenation process are studied. it is found that the (2LiNH(2) + MgH(2)) mixture has a higher rate for hydrogen release, slower rate for approaching a certain percentage of its equilibrium pressure, higher activation energy, and more NH(3) emission than the (LiNH(2) + LiH) mixture, On the basis of the phenomena observed, the reaction mechanism for the dehydrogenation of the (2LiNH(2) + MgH(2)) system has been proposed for the first time. Approaches for further improving the hydrogen storage behavior of the (2LiNH(2) + MgH(2)) system are discussed in light of the newly proposed reaction mechanism. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.