Carbon nanotubes (CNTs) have been synthesized over Ni-MgO and Ni-Sm-Mg catalysts by decomposition of CH4 at 923 K. The addition of Sm into Ni-MgO catalyst promotes its catalytic activity and lifetime. The yield of CNTs obtained over the optimized Ni-Sm-Mg catalyst reaches 1260wt% relative to the weight of the catalyst, which is more than 4 times that of the Ni-MgO catalyst. The possible interaction between Sm and Ni species is discussed.