Doping effects of manganese(Mn) on catalytic performance and structure evolution of Ni Mg O catalysts for synthesis of multi-walled carbon nanotubes(MWCNTs) from methane were investigated for the first time. Addition of Mn in Ni Mg O catalyst can greatly improve the MWCNTs yield. Mn0.2Ni Mg O catalyst among the tested ones gives the highest MWCNTs yield as 2244%, which is two times higher than that of the catalyst without Mn. The structure evolution, reduction behaviors and surface chemical properties of Mn Ni Mg O catalysts with various Mn contents were studied in detail. It was found that the stable solid solution of Ni Mg O2 formed in Ni Mg O catalyst was disturbed by the addition of Mn. Instead, another solid solution of Mn Mg6O8 is formed. More amount of Ni can be reduced and dispersed on the catalyst surface to be acted as active sites. Importantly, the changes of Ni content on the surface are correlated with the Ni particle size and the outer diameter of MWCNTs, suggesting the controllable synthesis of MWCNTs over Mn Ni Mg O catalysts. Doping effects of manganese (Mn) on catalytic performance and structure evolution of Ni Mg O catalysts for synthesis of multi-walled carbon nanotubes (MWCNTs) from methane were investigated for the first time. Addition of Mn in Ni Mg O catalyst can substantially improve the MWCNTs yield. Mn0.2NiMgO catalyst among the tested ones gives the highest MWCNTs yield as 2244%, which is two times higher than that of the catalyst without Mn. The structure evolution, reduction behaviors and surface chemical properties of Mn NiMgO catalysts with various Mn contents were studied in detail. It was found that the stable solid solution of Ni Mg O2 formed in Ni Mg O catalyst was disturbed by the addition of Mn. Instead, another solid solution of Mn Mg6O8 formed. Ni can be reduced and dispersed on the catalyst surface to be acted as active sites. Importantly, the changes of Ni content on the surface are correlated with the Ni particle size and the outer diameter of MWCNTs, suggesting the c ontrollable synthesis of MWCNTs over Mn Ni Mg O catalysts.