Ultraviolet (UV) and visible light active photocatalysts, 13-20 nm in size, were prepared by doping iron into anatase TiO2 (Fe/Ti at. ratio: 0.11% and 0.49%). Greater Fe dosage led to stronger light absorbance in both UV and visible regions, and also to generally better photocatalytic activity. Fe2+ and Fe3+ coexisted in 0.11% Fe-TiO2, while only Fe3+ existed in 0.49% Fe-TiO2. A dramatic change in the molecular environment of Fe was observed after the doping process; from cubic (Fe3O4) and trigonal (Fe2O3) structures into tetragonal TiO2. Different Fe speciation in catalysts led to different kinetics for methylene blue photocatalytic degradation.