Tungsten oxide (WO3) thin films were prepared by an electron beam deposition technique. Films were deposited onto fluorine-doped tin oxide (FTO)-coated glass substrates maintained at 523 K. The as-deposited films were found to be amorphous and crystallized after annealing at 673 K. The electrochromic and optical properties, structure, and morphology are strongly dependent on the annealing conditions. Cyclic voltammetry (C-V) was carried out in the potential range -1 to +1 V. Before and after colouration, the films were characterized by measuring transmittance and reflectance. The colouration efficiencies at 630 nm are about 39.4 cm(2) C-1 and 122.2 cm(2) C-1 for amorphous and crystalline films respectively. An investigation of self-bleaching for the coloured film revealed that the film fades gradually over time. (C) 2007 Elsevier B.V. All rights reserved.