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 C2H2 over MgO supported Fe-Mo bimetallic catalyst at 800 degreesC. 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 Al2O3 Support material. This work indicates that MgO is useful support material to realize the synthesis of high-quality SWNTs at high yield using C2H2 carbon source. (C) 2003 Elsevier B.V. All rights reserved.