High-quality single-walled carbon nanotubes (SWNTs) with few defects and very small amount of amorphous carbon coating have been produced by catalytic decomposition of C 2H 2 over MgO supported Fe–Mo bimetallic catalyst at 800 °C. The diameters of SWNTs are in the range of 0.80–2.43 nm from Raman analysis. The use of MgO support facilitates a large-scale synthesis of SWNTs with a smaller diameter compared with Al 2O 3 support material. This work indicates that MgO is useful support material to realize the synthesis of high-quality SWNTs at high yield using C 2H 2 carbon source.