NiMgAl mixed oxides obtained by thermal decomposition of layered double hydroxides have been studied in the reaction of hydrocarbon steam reforming for producing hydrogen. The effect of synthesis parameters such as method of introduction of active species, amount of components and thermal treatments (calcination and reduction) on structure and reactivity of these materials has been elucidated. Samples have been characterized by N-2 adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) and elemental analysis. Synthesis parameters have an important influence on metal-support interaction, when stronger are metal-support interactions more favourable is the catalyst structure for obtaining highly and finely dispersed nickel particles. Catalyst performance was strongly related to the nickel particle size. The support and its properties seem to play a key role in the performance of the hydrotalcite-derived catalysts. (c) 2007 Elsevier B.V. All rights reserved.