A novel class of visible-light-activated TiO2 photocatalysts were prepared by direct hydrolysis of tetrabutyl titanate through iodine-doping. When calcination temperature is at 673 K, these nanoparticles (mean diameter of similar to 5 nm) show stronger absorption in the 400-550 nm range with a red shift in the band gap transition and significantly higher photocatalytic activity than pure TiO2 prepared by the same procedure and Degussa P-25 titania nanoparticles in aqueous phenol solution under visible light irradiation (lambda > 400 nm). Furthermore, I-doped TiO2 (673 K) still showed pronounced photocatalytic activity under UV and visible light irradiation.