Co-doping of TiO2 with Cr and Sb was recently found to have a beneficial effect on the photocatalytic activity under visible-light irradiation. With the present comparative standard and hybrid density functional study we get new insight into the electronic structure of the system and provide a theoretical support to the experimental findings. Hybrid DFT better describes (i) the Cr d states splitting and thus the semiconducting properties of the Cr-doped system, and (ii) the localized nature of the Ti3+ states produced by Sb doping. An electron transfer from the Sb-induced states to the Cr 3d levels is considered to be the reason for the enhanced photostability of the co-doped Cr/Sb system. (C) 2008 Elsevier B. V. All rights reserved.