A hydrogen storage material was prepared by mechanical milling of LiNH2/MgH2 (2:1) mixture. Phase identification and structural investigation indicated that the initial dehydrogenation leads to the formation of a novel Li-Mg-N-H phase. The reversible reaction between the novel phase and Mg(NH2)(2)/LiH mixture in the following de-/rehydrogenation cycles at 200 degrees C leads to a stable hydrogen uptake capacity of similar to 4.3 wt%. The dehydrogenation of the material can be performed at lower temperatures, but with markedly slow kinetics and lowered hydrogen uptake capacity. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.