A hydrothermal treatment was employed to implant three types of metal ions (Fe, Co, and Ni) into commercial TiO2 photocatalysts for improving the photocatalytic reactivity of methylene blue (MB) under visible light irradiation. Nitrogen physisorption measurement indicated that surface areas and porosities of metal-doped titania powders still maintain an identical value, compared to the starting material. The diffuse reflection spectra of metal-doped titania reflected a light absorption edge, shifting to the visible light range of approximately 400-700 nm. According to the Kubelka-Munk plot, the optical band gaps were found to have the following order: Fe doping(2.98 eV) > Co doping(2.88 eV) > Ni doping(2.63 eV), based on the fixed dopant concentration. A Langmuir-Hinshelwood model was used to investigate the photocatalytic activity for removing MB from the liquid phase. It was found that the photodegradation activity has an increasing trend with the decreasing optical band gap. (c) 2007 American Vacuum Society.