Recent laboratory studies have shown that metal nanoparticles-decorated single-walled carbon nanotubes (SWCNTs) can be used to detect carbon monoxide (CO) gases at room temperature, which is known not able to be adsorbed on pure SWCNTs. In this paper, we investigated the Rh-decorated (8,0) SWCNT and its interaction with CO gases by using density functional theory (DFT) methods. Upon Rh atom adsorption, the conductivity of the (8,0) SWCNT and the atomic charges of some carbon atoms around Rh atom are enhanced dramatically. The Rh-adsorption may be thought of as providing "activated" carbon-sites of adsorbing foreign species. Both the Rh-site and the "activated" C-sites are considered as reactivity sites for the adsorption of CO gases. The binding energy is larger for CO-adsorption on the Rh-site than on the "activated" C-sites. Since the interaction between CO gases and the Rh-site is very strong, the Rh-decorated SWCNT is not reusable for CO gases detecting due to the large binding energy. On the other hand, the CO gases can also be adsorbed on the "activated" C-site with the binding energy of about -0.80 eV and 0.12 electrons transfer. The electronic properties have changed dramatically upon the CO gases. These calculation results are useful not only to explain the sensing mechanisms but also to evaluate the potential for SWCNTs-based sensing materials at room temperature. (C) 2008 Elsevier B.V. All rights reserved.