Na[Al(NH2BH3)(4)], a mixed-metal amidoborane, was synthesized by ball-milling (solid method) and the chemical reaction in THF (solution method). Solid method has a tendency to remain unreacted NaAlH4 and AB. In the solution method, the partial decomposition of Na[Al(NH2BH3)(4)] would proceed during mixing in THF. The local structural characterization of as-synthesized material was performed by MAS NMR and FT-IR. While Na[Al(NH2BH3)(4)] desorbed hydrogen in two steps as reported, the results of structural characterization suggested that the hydrogen desorption in the 2nd step would originate from the Al-N-B H phase. Effect of hydrogen pressure during ball-milling was also investigated for nNH(3)BH(3)-NaAlH4 (n = 1, 4) composites. In the case of n = 4, Na[Al(NH2BH3)(4)] was formed under both Ar and H-2 atmosphere. However, in the case of n =1, Na[Al(NH2BH3)(4)] only formed under H-2 atmosphere, whereas most of H-2 was desorbed during ball-milling under Ar atmosphere. Thus, the hydrogen pressure is necessary for the synthesis in the case of n = 1. Potential energy diagram of AB-NaAlH4 system was described. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.