The composites of (NaBH4+2Mg(OH)(2)) and (LiBH4+2Mg(OH)(2)) without and with nanometric Ni (n-Ni) added as a potential catalyst were synthesized by high energy ball milling. The ball milled NaBH4-based composite desorbs hydrogen in one exothermic reaction in contrast to its LiBH4-based counterpart which dehydrogenates in two reactions: an exothermic and endothermic. The NaBH4-based composite starts desorbing hydrogen at 240 degrees C. Its ball milled LiBH4-based counterpart starts desorbing at 200 degrees C. The latter initially desorbs hydrogen rapidly but then the rate of desorption suddenly decelerates. The estimated apparent activation energy for the NaBH4-based composite without and with n-Ni is equal to 152 +/- 2.2 and 157 +/- 0.9 kJ/mol, respectively. In contrast, the apparent activation energy for the initial rapid dehydrogenation for the LiBH4-based composite is very low being equal to 47 +/- 2 and 38 9 kJ/mol for the composite without and with the n-Ni additive, respectively. XRD phase studies after volumetric isothermal dehydrogenation tests show the presence of NaBO2 and MgO for the NaBH4-based composite. For the LiBH4-based composite phases such as MgO, Li3BO3, MgB2, MgB6 are the products of the first exothermic reaction which has a theoretical H-2 capacity of 8.1 wt.%. However, for reasons which are not quite clear, the first reaction never goes to full completion even at 300 degrees C desorbing 4.5 wt.% H-2 at this temperature. The products of the second endothermic reaction for the LiBH4-based composite are MgO, MgB6, B and LiMgBO3 and the reaction has a theoretical H-2 capacity of 2.26 wt.%. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH4- and LiBH4-based composites is rather negligible. The n-Ni additive may not be the optimal catalyst for these hydride composite systems although more tests are required since only one n-Ni content was examined. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.