The catalyst LaNiO3 prepared by the auto-ignition method shows high activity, stability and a good resistance to carbon deposition for the CO2 reforming of methane reaction. We have shown that during temperature increase up to 700 degrees C under the presence of the reactants (CH4 + CO2), the perovskite phase was transformed into Ni-0 and La2O2CO3. Transmission electron microscopy (TEM) measurement performed after the reaction has shown that the average nickel particle size depends on the way the reaction is carried out, nickel particles are larger in the case of pre-reduced catalyst than in that of non-pre-reduced catalyst. When using a non-reduced precursor material, the introduction of the reactant at 700 degrees C instead of at room temperature leads to a lower activity, whereas the nickel particle size distribution is quite similar for the two experiments. To explain the differences in the catalytic activity, we can assume that the number of accessible sites is different, consequently the way the active species are generated is a key step for the reaction. (c) 2005 Elsevier B.V. All rights reserved.