The NaBH4 nanocrystals (NCs) were successfully synthesized by mechanically driven anion metathesis between LiBH4 and NaCl where the newly formed NaBH4 has an approximately 10 nm in size being in situ embedded in the buffering matrix of LiCl byproduct. These NaBH4 NCs obtained show significantly enhanced desorption properties with a reduction in onset temperature by 30%, over 6 times faster kinetics and nearly 4 times higher equilibrium pressure than those of micro-NaBH4. This novel mechanochemical approach can also be employed to prepare other borohydrides NCs such as KBH4. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.