Undoped and C-doped TiO2 thin films have been prepared by sol-gel process. Their structure and optical properties have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy. It has been observed that C dopants retard the transformation from anatase-to-rutile phase. Namely, C doping effect is attributed to the anatase phase stabilization. The optical analyses show that the optical band gap of anatase C-doped TiO2 decreases with increasing amount of C. Also, it is founded that C dopants have been shown to make TiO2 have a visible light photoresponse. (C) 2009 Elsevier B.V. All rights reserved.