Undoped and up to 0.23 at% Sn-doped TiO2 thin films and polycrystalline powders have been prepared by sol-gel process. Their structure, surface morphology. and optical properties have been investigated by XRD, DTA-TG, SEM and UV-VIS spectroscopy. It has been observed that Sn promotes the anatase to rutile phase transformation and forms a complete solid solution with rutile TiO2. It is found that incorporation of about 0.17 at% of Sn completely transforms anatase TiO2 to the rutile form at a calcination temperature as low as 500 degreesC. This is the lowest temperature reported so far for the anatase to rutile phase transition in sol-gel TiO2. Optical analyses show that the Fermi level of the Ti1-xSnxO2 solid solutions increases with increasing x. (C) 2003 Elsevier B.V. All rights reserved.