Polymer-stabilized cobalt(0) nanoclusters were prepared from the reduction of cobalt(II) chloride in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) stabilizer in methanol solution. PVP-stabilized cobalt(0) nanoclusters were found to be stable in solution and Could be isolated its solid material and characterized by TEM, XPS, FT-IR, and UV-visible electronic absorption spectroscopy. PVP-stabilized cobalt(0) nanoclusters were employed as catalyst in the hydrolysis of sodium borohydride and ammonia-borane, which have been considered as solid-state hydrogen storage materials for portable fuel cell applications. PVP-stabilized cobalt(0) nanoclusters were found to be highly active catalyst in both hydrolysis reactions, even at room temperature. Kinetic studies show that the catalytic hydrolyses of sodium borohydride and ammonia-borane are both first order with respect to catalyst and substrate concentration in aqueous medium. The effect of the NaOH concentration on the catalytic activity of the PVP-stabilized cobalt(0) nanoclusters in the hydrolysis of sodium borohydride was also studied. The activation parameters of these hydrolysis reactions were determined from the evaluation of the kinetic data. The PVP-stabilized cobalt(0) nanoclusters provide a lower activation energy for the hydrolysis of sodium borohydride both in aqueous medium (E-n = 63 +/- 2 kJ.mol(-1)) and in basic solution (E-a = 37 +/- 2 kJ.mol(-1)) compared to the value reported for bulk cobalt (E-a = 75 kJ.mol(-1)).