In this work the influence of the deposition conditions on the structural, electrical and optical properties of the ITO films was studied. Films were deposited by r.f. plasma sputtering technique in Ar and varying Ar+O-2 gas mixtures, with and without substrate heating. Transmittance and reflectance of the films were measured in the range 350-2500 nm; the refractive index (n) and the extinction coefficient (k) were calculated by the spectral data simulation. The sheet resistance of the films was measured by four-point probe method. X-ray diffraction analysis was performed to study the texture of the films. Threshold behaviour was observed in the optical and electrical properties of ITO films deposited in Ar+O-2 atmosphere at a certain oxygen concentration determined by a fix combination of all other deposition conditions. A schematic diagram for the change of the film properties versus composition was suggested, which explains the obtained results. (c) 2007 Elsevier B.V. All rights reserved.