InOx thin films were grown by dc magnetron sputtering. Structural and morphological investigations carried out by XRD and AFM showed a strong correlation between crystallinity, surface topology and ozone sensitivity. The electrical conductivity exhibited a large change of six orders of magnitude during the processes of photoreduction/oxidation. It was concluded that it is mainly the grain size variation that determines the sensitivity of InOx films against ozone. (c) 2006 Elsevier B.V. All rights reserved.