An ordered mesoporous " one-pot " nickel-alumina catalyst (5 wt% Ni) was synthesized using the evaporation-induced self-assembly method. Compared to an impregnated and to a non-porous catalysts, the ordered "one-pot" Ni-alumina sample displayed, after in-situ reduction, the highest and the most stable catalytic performances along 40h of run at 800°C in combined steam and dry reforming of methane, with conversion and selectivity values close to the thermodynamic expected-ones. Both the confinement of well-dispersed Ni-nanoparticles within the structured Al2O3 framework and the strengthened Ni-support interaction compared to other catalysts are shown to be key factors accounting for the high catalytic activity and stability. Contrarily to alumina that appears as an effective support of Ni for catalytic combined methane reforming, neither mesoporous (SBA-15) nor macroporous (CeliteS, diatoms) silica are appropriate ones due to rapid deactivation by partial reoxidation of the metallic Ni 0 active phase in the conditions of reaction.