Formation of single-layered (SL) carbon tubes by the are-evaporation method has been studied using a series of rare-earth elements (Sc, Y, and La through Lu, excluding Pm) as catalysts. Electron microscopy of soot materials revealed that Y, La, Ce, Pr, Gd, Tb, Dy, Ho, Er, and Lu (including Gd, Y, La and Nd, which are already reported to be active catalysts) assisted the formation of SL tubes. The tube length ranged from 10 to 100 nm depending on the catalytic activity of the elements, while diameters were 1.8-2.1 nm regardless of the elements. Y, La, and Ce, which were the three rare-earth elements with the lowest vapor pressures, showed the highest activity among the elements investigated. The relation between the manifestation of the catalytic activity and the volatility of the elements was discussed.