Transparent conductive and WO3 clectrochromic thin films were deposited by spray pyrolysis technique. The films were deposited using solutions Of WCl6 in dimethylformamide on SnO2:F (FTO) substrates with different sheet resistances. Noticeable effects of substrate on structural, morphological and optical properties of the WO3 films and on its clectrochromic behavior are presented and discussed. Hexagonal and monoclinic WO3 structures were obtained on amorphous glass substrates; also the monoclinic structure on polycrystalline FTO substrates was obtained. Cyclic structural changes during the colored and blanched states were found from XRD and electron diffraction result analysis: The hydrogen tungsten bronze in the tetragonal phase after the hydrogen extraction change to the original WO3 monoclinic phase. (c) 2006 Elsevier B.V. All rights reserved.