The Cu-doped tungsten bronze (TB) type potassium niobate K2Nb4O11 was synthesized by solid-state reaction method in air. The crystal structure and morphology of the prepared samples were confirmed by X-ray diffraction analysis and scanning electron microscope. The photocatalytic activity of the prepared samples was evaluated using acid red G as a model organic compound and the photocatalytic reaction belongs to the first order kinetics. The results show that Cu-doping significantly increased the photocatalytic activity of K2Nb4O11 catalyst when the concentration of Cu-doped was lower, but the photocatalytic activity of the catalyst was decreased when the concentration of Cu-doped was higher. Although the surface areas of the 0.2 wt.% Cu-doped K2Nb4O11 and the 0.5 wt.% Cu-doped K2Nb4O11 are very lower, the photocatalytic activities of these compounds are close to that of TiO2-P25. Copper doping is good for the compounds to form tetragonal TB structure and improving the crystallinity of the compounds. The diffuse reflectance spectrum of Cu-doped K2Nb4O11 showed a red shift. X-ray photoelectron spectroscopy analysis confirmed that the niobium with mixed valence state exists in the crystal structure of the compound K2Nb4O11. The effects of the Cu-doped and the mixed valence state of niobium on the photocatalytic activity of the catalyst were discussed. (c) 2006 Elsevier B.V. All rights reserved.