This paper describes the effect of magnesium (Mg) addition on sodium borohydride (NaBH(4)) synthesis from anhydrous borax (Na(2)B(4)O(7)) in the presence of the hydrogen atmosphere. NaBH(4) synthesis has been investigated at a temperature of 550 degrees C and 25 bar hydrogen pressure experimentally. The reactions were carried out in a stainless steel batch reactor placed in a vertical furnace. The extent of reaction was monitored by observing pressure decrease in the system. Aqueous ammonia was used to extract NaBH(4) from the reaction mixture. Highly pure sodium borohydride was obtained after evaporation of the solvent. Characterization of the product was made by the X-ray powder pattern studies. It was found that the amount of Mg plays an important role in NaBH(4) formation. Increasing the amount of Mg resulted in appreciable increase in NaBH(4) formation. The NaBH(4) yield reached in the experiments was found to be 93% in a single batch process. Crown Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.