We describe a method tuning the band-gap energy (E-g) of visible light sensitive TiO2-xCx nanoparticle. E-g tends to become smaller with the increase in the amount of carbon dopant in TiO2-xCx nanoparticle due to the increase in excess electrons. Photo-catalytic oxidative activity, however, did not depend on only the value of E-g, but also the energy level of valence band. TiO1.96C0.04 nanoparticle having E-g of 2.6 eV showed outstanding performance in oxidative decomposition of phenol under the irradiation of visible light. (C) 2010 Elsevier B.V. All rights reserved.