Photocatalytic properties of SnO2/TiO2 (TiO2 overcoated with SnO2) heterojunction system were investigated. It was found that some SnO2/TiO2 thin film stacks have photocatalytic activities and their efficiency depends on the photoactivity of the TiO2 film and also SnO2 film properties even though the SnO2 film itself does not have photocatalytic activity. The experimental results revealed that the interface between TiO2 and SnO2 acts as a potential barrier for the carriers photo-generated in the TiO2 and the photo-generated species pass through the SnO2 overlayer depending on the SnO2 film characteristics. (c) 2005 Elsevier B.V. All rights reserved.