A series of nano-sized Ni/Al 2 O 3 and Ni/La–Al 2 O 3 catalysts that possess high activities for NH 3 decomposition have been successfully synthesized by a coprecipitation method. The catalytic performance was investigated under the atmospheric conditions and a significant enhancement in the activity after the introduction of La was observed. Aiming to study the influence of La promoter on the physicochemical properties, we characterized the catalysts by N 2 adsorption/desorption, XRD, H 2 -TPR, chemisorption and TEM techniques. Physisorption results suggested a high specific surface area and XRD spectra showed that nickel particles are in a highly dispersed state. A combination of XRD, TEM and chemisorption showed that Ni 0 particles with the average size lower than 5.0nm are always obtained even though the Ni loading ranged widely from 4 to 63%. Compared with the Ni/Al 2 O 3 catalysts, the Ni/La–Al 2 O 3 ones with an appropriate amount of promoter enjoy a more open mesoporous structure and higher dispersion of Ni. Reduction kinetic studies of prepared catalysts were investigated by temperature-programmed reduction (TPR) method and the fact that La additive partially destroyed the metastable Ni–Al mixed oxide phase was detailed.