In this paper, we developed an easy and simple method (high-energy ball milling) for recycling NaBO2 (the hydrolysis byproduct) back to NaBH4 by a reaction with MgH2. To optimize the yield of NaBH4, we investigated the effect of four parameters, e.g. the ball milling time, the molar ratio of MgH2/NaBO2, H2 pressure and addition of methanol, on the NaBH4 regeneration. Accordingly, the maximum yield of NaBH4 (89 wt. %) was achieved. The mechanism of NaBH4 regeneration has been discussed. It is indicated that the NaBH4 formation involves a two-step substitution in which NaBOH2 is an intermediate confirmed by solid-state nuclear magnetic resonance (NMR).