A novel N-doped TiO2 with high visible light photocatalytic activity was obtained by treating nanotube titanic acid (NTA) in NH3 flow and investigated by means of XRD, TEM, ESR and XPS. The ESR results revealed that the visible light photocatalytic activity is originated from N-doping into TiO2 with the forming of triplet paramagnetic species, the higher triplet paramagnetic species concentration, the better visible light photocatalytic behavior. (c) 2006 Elsevier B.V. All rights reserved.