High-energy ball milling was employed to regenerate spent-sodium borohydride, i.e., mainly the sodium metaborate (NaBO2), back to sodium borohydride (NaBH4) by a reaction with magnesium hydride (MgH2). The samples were characterized using scanning electron microscopy (SEM), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy, X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy. In general, as the ball-milling duration increases, the yield of NaBH4 increases accordingly and leads to an extreme value of 76%, when MgH2 in stoichiometric excess by 40% was initially present in ball mills. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.