This paper reports the influence of In2O3 film Structure on gas-sensing characteristics measured in steady state and transient modes. Films were deposited by spray pyrolysis from InCl2-water solutions. Correlation between gas-sensing parameters and structural parameters such as film thickness (20-400 nm), grain size (10-70 nm), refractive index and film texture (I(400)/ I(222)) were established. It was shown that grain size and porosity are the parameters of In2O3 films that best control gas response to ozone. In the detection of reducing gases, the influence of film structure is less important. Decreases in film thickness, grain size and degree of texture are the best way to decrease time constants of the gas response of In2O3-based gas sensors. (C) 2004 Elsevier B.V. All rights reserved.