The Ni/Mg/Al catalysts were prepared from the calcination and reduction of hydrotalcite-like compounds containing Ni, Mg and Al, and applied to the steam reforming of tar from pyrolysis of biomass. The dependence of the composition and reduction pretreatment conditions on the catalytic performance was investigated. It is found that the Ni/Mg/Al catalyst with optimized composition of Ni/Mg/Al = /66/25 exhibited much higher activity, resistance to coke deposition, and stability than Al2O- and MgO-supported Ni catalysts. The catalyst characterization using XRD, TPR, N-2 and H-2 adsorption, and TEM indicates that the Ni/Mg/Al catalyst after the reduction has a nanocomposite structure of Ni metal particles (about 8.5 nm) and Mg(Ni. Al)O particles (about 11.5 nm). Even after the catalytic use, the nanocomposite structure was maintained. High performance of the Ni/Mg/Al catalyst including the suppression of the aggregation of the metal particles can be caused by the nanocomposite structure. (C) 2010 Elsevier B.V. All rights reserved.