Anatase-type TiO2 (titania) doped with iron up to 19.8 mol% was directly formed as nanometer-sized particles from acidic precursor solutions of TiOSO4 and Fe(NO3)(3) by simultaneous hydrolysis, under mild hydrothermal conditions at 180degreesC. Iron content in the anatase-type TiO2 was much less than that of the starting composition of the precursor solutions because of slower hydrolysis rate of Fe(NO3)(3) than that of TiOSO4 at 180degreesC. The XRD data, TEM selected-area diffraction patterns, and Mossbauer effect measurement showed that iron(RI) formed a solid solution in the anatase-type TiO2 precipitates and that there was no iron oxide precipitated as secondary phase without making a solid solution with TiO2 present in the precipitates. Doping of Fe2O3 into TiO2 shifted the phase transformation from anatase-type to rutile-type structure to a low temperature. On the phase transformation from anatase to rutile, iron oxide was precipitated as Fe2TiO5 (pseudobrookite) phase. When the iron content was increased in the anatase phase, onset of optical absorption shifted to longer wavelengths, and absorption in the UV-light region and in the visible-light region over 400-600 nm clearly appeared in the diffuse reflectance spectra of the as-prepared Fe(III)-doped TiO2.