TiO2 thin films of 200-300 nm thickness were deposited by d.c. magnetron sputtering onto glass substrates from a semiconducting TiO2-x target in pure Ar using pressures between 0.1 and 1.0 Pa. The obtained TiO2 coatings are transparent and have refractive indices between 2.5 and 1.9. Post deposition heat treatment at different temperatures was perfanned to achieve crystallization of anatase TiO2. The as-deposited and heat treated films were examined with UV-VIS (transmission), SEM and XRD to investigate the influence of the argon pressure during deposition on the structural development during heat treatment. Additionally, the photocatalytic activity of the films was tested by measuring the decomposition rate of ethanol in a controlled gas atmosphere simulating air, and was related to their respective microstructures. (c) 2005 Elsevier B.V All rights reserved.