A simple. economical. chemical bath method for depositing tungsten oxide films has been developed. The films have been prepared from aqueous solution containing Na2WO4 center dot 2H(2)O and diethyl sulfate in slightly acidic media at 90-95 degrees C on fluoride doped tin oxide substrates (FTO). The X-ray analysis clearly showed that the films do not correspond to any known tungsten oxide with its experimental d-values and in the text the composition is denoted as WOx. The thin films durability was tested in aqueous solution of LiClO4 (0.1 mol dm(-3)) for about 7000 cycles followed by cyclic voltammetry which confirmed that the coated material is highly stable. The optical transmittance spectra of colored and bleached states showed significant change in the transmittance, which make these films favorable for electrochromic devices. (c) 2007 Elsevier B.V. All rights reserved.