The Mn promoted Ni catalysts were developed and applied in CO methanation reaction. The 10%Ni/SiO2 catalyst exhibits poor initial CO conversion (32.8%) and rapid deactivation with the highest methane selectivity during CO methanation reaction. In contrast, the Mn 4%Mn-10%Ni/SiO2 catalyst shows dramatically increased initial CO conversion, which is up to 94.5% with 90.0% methane selectivity. Besides, the apparent activation energy, Ea value, of 4%Mn-10%Ni/SiO2 was calculated to be 73.1 kJ/mol according to Arrhenius equation, which is much lower than that of 10%Ni/SiO2 catalyst as 139.1 kJ/mol. Based on various characterization results, including in situ XPS and in situ CO-DRIFTS, it is found that the added Mn significantly improves the dispersion of the supported nickel, suppresses the sintering of nickel particles and forms more adsorbed CO species of three-fold carbonyl species, resulting in higher CO conversion and good stability during CO methanation reaction.