Transparent TiO2 thin films were successfully prepared on glass substrates by using spray pyrolysis technique. The films are amorphous at deposition temperatures up to 450 C. Starting at about 550 C, the films are partially crystallized (anatase phase). The prepared films have good homogeneity with some porosity, which is suitable for the photocatalytic applications. By using high performance liquid chromatography (HPLC) technique, it was possible to prove the photocatalytic properties of TiO2 thin films. The procedure uses basically the UV-catalytic transformation of methanol traces in water to methanal. Deposition parameters such as deposition temperature and spray time are varied to investigate the effect on the photocatalytic activity of the prepared films. (C) 2002 Published by Elsevier Science B.V.