In this paper, Ni-Mn catalysts supported on mesoporous nanocrystalline γ -Al₂O₃ were prepared and employed in carbon dioxide reforming of methane for the production of synthesis gas. The physicochemical properties of the catalysts were determined by XRD, BET, TPO and SEM techniques. The obtained resultsrevealed that the Mn-promoted catalysts exhibited higher activity and stability and lower degree of carbon formation compared to unpromoted nickel catalyst. The catalytic results showed that the 10 (wt%) Ni-3 (wt%) Mn/Al₂O₃ catalyst possessed the highest catalytic activity. The XRD results confirmed that the addition of Mn improves the dispersion of the active metal species on the catalyst or incorporates into the support due to a decrease in the crystallite size of Ni and consequently causes an increase in Ni dispersion. The 10 (wt%) Ni-3(wt%) Mn/Al₂O₃ catalyst was stable during 20 hour on stream without any decrease in methane conversion