In order to improve the photocatalytic activity, iodine cation and anion were successfully doped into TiO2 nanotubes by using cathode reduction and anodization, as evidenced from X-ray photoelectron spectroscopy results. Field-emission scanning electron microscopy images suggest that electrochemical method is efficient to dope nonmentals and advantageous to keep the morphological integrity of TiO2 nanotubes. I-doped TiO2 nanotubes show the high photocurrent and photocatalytic activity under UV-vis irradiation. First-principle calculation results indicate that some new bands appear in the band gaps and are beneficial for photogenerated carriers migration. For cation-doped TiO2, a strong interaction between the electrons in I 5p orbitals and in Ti 3d orbitals occurred and results in the CB shifting downwards. The band potentials of cation-doped TiO2 shift downwards to a larger extent and thus the VB has a stronger oxidative power than undoped and anion-doped TiO2. (C) 2009 Elsevier Ltd. All rights reserved.