Temperature-programmed reduction (TPR) profiles recorded on calcined Ni/Al2O3 catalysts exhibiting the same Ni(II) surface density (3 Ni2+ nm−2) suggest that nickel speciation and reducibility are significantly influenced by the specific surface area and texturalproperties of aluminas, and by their stability toward water during impregnation. Limiting the dissolution of Al2O3 and protecting Ni2+ ions are required to increase the reducibility of Ni/Al2O3 catalysts, especially for mesoporous aluminas presenting a high specific surface area.