In this work we present a calorimetric study of NaBH(4) hydrolysis in the presence of Co(3)O(4). NaBH(4) can be utilized as source of a high purity hydrogen generated by the hydrolysis reaction (BH(4)(-) + 4H(2)O -> B(OH)(4)(-) + 4H(2)) which is easily controlled by catalysts. A modified Setaram Titrys microcalorimeter was used to determine the enthalpy of hydrolysis in a system where water excess is added to pure solid NaBH(4) as well as to solid NaBH4 mixed with Co(3)O(4). Effects of different amounts of water and NaOH (solid and solution) additions on the rate of hydrolysis reaction were also investigated. Heats evolved under different experimental conditions were always about 240 kJ mol(-1). Lower amount of water resulted in lower reaction rate. The addition of NaOH solution increased the catalytic activity compared to the addition of the same amount of solid NaOH. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.