Light-elemental amides and imides are recently regarded as potential candidates for high-performance hydrogen storage materials. In this studies, the single phases magnesium amide (Mg(NH2)(2)) and magnesium imide (MgNH) were successfully prepared by solid-gas reactions of MgH2 with ammonia at 613 K and 653 K, respectively. Subsequently, Mg(NH2)(2) was mixed with different molars of MgH2 or LiH in order to systematically investigate the dehydriding properties. With increasing temperature, the mixtures of Mg(NH2)(2) and MgH2 desorb ammonia at approximately 630 K, similar to the decomposition reaction of Mg(NH2)(2) alone. On the other hand, the mixture of Mg(NH2)(2) and 4 M of LiH desorbs only hydrogen during heating because of the "ultra-fast" reaction of LiH with ammonia from Mg(NH2)(2), unlike MgH2. (C) 2004 Elsevier B.V. All rights reserved.