Electrochromic thin films of tungsten oxide have been prepared on a flexible substrate by the sol-gel method. A solution of WOCl4/(PrOH)-Pr-i was used as precursor. Films were synthesized by dip-coating on commercially available PET (polyethylene terephtalate)/ITO (indium tin oxide) substrates. Owing to the ITO sensitivity to acid attack, no pure WO3 coating could have been obtained. Some ITO grains separate during the dip-coating process leading to a mixture of WO3 and ITO. Coatings surface and morphology was studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy. Composition in depth was investigated by SEM pictures of cross-section and by secondary ions mass spectroscopy. The electrochromic properties of these films (area = 25 cm(2)) were analyzed in a three-electrodes cell with a 1 M LiClO4/propylene carbonate electrolyte. Though the structure is not yet fully understood, these coatings exhibit good electrochromic properties.