A convenient method was developed to synthesize NaBH 4 by the reaction of MgH 2 with Na 2 B 4 O 7 through ball milling at room temperature. In order to improve the sodium borohydride yield, Na compounds were added to compensate the Na insufficiency in reactants when MgH 2 instead of NaH was used as the reducing agent. It was found that Na 2 CO 3 addition was better than NaOH or Na 2 O 2 addition in increasing the borohydride yield.