A modified sol-gel method was employed to synthesize metal-doped TiO2 with varied dopant concentrations using titanium butoxide and metal nitrate hydrate as the precursors and hydrothermal posttreatment. The prepared samples were characterized by XRD, XPS, TEM, BET, UV-vis/diffuse reflectance, PZC measurement, Raman spectroscopy, photoluminescence, and fluorescence lifetime, while the photocatalytic activities were tested using benzoic acid as the model compound. Ga-doped TiO2 exhibits the highest photoactivity among the prepared metal-doped TiO2 photocatalysts. This is most likely due to the good dispersion of Ga dopant onto the surface of TiO2, adequate surface area, and decrease of recombination center on the surface of Ga-doped TiO2 photocatalyst. The optimum dopant concentration was found to be 0.1 wt % for Ga-doped TiO2.