Amorphous nickel catalysts were synthesized by reducing the nickel(II) species in an aqueous NaBH4/NH3BH3 solution with and without L-arginine. The nickel catalyst with L-arginine maintains relatively high activity for hydrolysis of NH3BH3 to generate a stoichiometric amount of hydrogen with the cycle number up to 11 (827 mL s(-1) (mol-Ni)(-1) at the 11th cycle with L-arginine = 35 mg), while the reaction rate in the presence of the bare nickel catalyst was relatively low through the cycle number up to 11 (232 mL s(-1) (mol-Ni)(-1) at the 11th cycle). After catalytic reaction, the nickel catalyst with L-arginine possesses the high dispersion (diameters of nickel nanoparticles <5 nm), while the agglomerate of nickel in the bare nickel catalyst is observed. The results indicate that L-arginine maintains the dispersion of nickel nanoparticles (diameters of nickel nanoparticles <10 nm), leading to higher activity against cycle tests than the bare nickel catalyst. (C) 2012 Elsevier B.V. All rights reserved.