KNb3O8 and HNb3O8 nanobelts were prepared by hydrothermal synthesis. The characteristics of samples were investigated by XRD, SEM, and UV-vis diffuse reflectance spectroscopy. The KNb3O8 and HNb3O8 nanobelts exhibited much higher activities for CO2 photoreduction to methane than commercial TiO2 (Degussa P25), and the KNb3O8 and HNb3O8 particles prepared by conventional solid state reaction. It was also found that either the HNb3O8 nanobelts or the HNb3O8 particles performed better than the corresponding KNb3O8 counterpart. It is proposed that the nanobelt-like morphology and the protonic acidity contribute to the higher photocatalytic activity of the HNb3O8 nanobelts. (C) 2011 Elsevier B.V. All rights reserved.