The universal behavior of low-temperature thermal conductance in single-walled carbon nanotubes is revealed within the framework of the Landauer theory of heat transport. The phonon-derived thermal conductance is quantized as a universal value of pi(2) k(B)(2)T/3h in the lowtemperature limit, T-->0, independent of radius or chirality. The temperature dependence follows a single curve given in terms of temperature scaled by the energy gap of the lowest optical mode. In contrast, the electronic contribution to thermal conductance at low temperature is found to be strongly dependent on the tube geometry responsible for the electronic states. (C) 2004 Elsevier B.V. All rights reserved.