Two series of Nix% (x: 5–10 wt%) and Ni5%M5% (M: Ca or Mg) containing mesoporous Al2O3 catalysts were prepared by “one-pot” synthesis following an evaporation-induced self-assembly (EISA) method. After reduction, the catalysts showed very high Ni dispersion within the structured oxide matrix giving high activities and long-term stabilities in combined steam and dry reforming of methane (CSDRM) carried out at 800 °C. Both the increase of Ni content and the addition of Mg (or Ca) are beneficial to performances, with activity levels reaching the maximum-expected thermodynamic ones for Ni10%Al2O3. In the Mg (or Ca) free catalysts, a relationship between nickel content, reactivity level and carbon deposition is found. Nevertheless, carbon formation is not detrimental to catalytic stability due to formation of carbon nanotubes only outside the nickel containing alumina grains. Addition of Ca or Mg suppresses to a great extent carbon deposition and leads to high selectivity towards the targeted CSDRM reaction, with almost no occurrence of side reactions. The remarkable thermal stability of the ordered-mesoporous alumina structure (along 40 h of run) along with the stabilization of well-dispersed Ni0 within the alumina matrix are shown to be key factors accounting for the excellent long term catalytic performances in spite of the harsh conditions (temperature and steam) imposed by the reaction