We investigated the optical emission from a freestanding individual multiwall carbon nanotube through which a current is passing. Since the emission spectra are well represented by Planck's black body radiation law, the optical emission from the nanotubes is assigned to thermal radiation. The average temperature for the sublimation of the nanotubes is estimated to be similar to 2540 K from the fitting. Another emission component in the visible region has also been found. The optical and the thermal radiations using Joule heating of the nanotube can be used as a novel nanoscale-processing tool. (C) 2004 Elsevier B.V. All rights reserved.