Composite NaNH2-NaBH4 (molar ratio of 2/1) hydrogen storage materials are prepared by a ball milling method with various ball milling times. The compositions and hydrogen generation characteristics are investigated by means of X-ray diffraction (XRD) and thermo gravimetric-differential thermal analysis (TG-DTA). The structural characteristics imply that ball milling produces a new phase of Na-3(NH2)(2)BH4, and mechanical energy accumulated in the ball milling process may be responsible for the phase change of Na3(NH2)2BH4. TG-DTA demonstrates that the phase change temperature of the composite NaNH2-NaBH4 (2/1) ball milled for 16 h is 141.8 degrees C, and the melting point is 197.3 degrees C; below 400 C, composite hydrogen storage material is mainly decomposed to give hydrogen and Na3BN2; while above 400 degrees C, the previous by-product Na3BN2 continues to decompose so as to give metal Na gradually. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.