Self-organized macroporous tungsten trioxide (WO3) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10 mm x 25 mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO3 films with a thickness of ca. 350 nm are formed. The film shows a connected network with average pore size of 100 nm and a pore wall thickness of approximately 30 nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1 M H2SO4, the macroporous WO3 films show enhanced electrochromic properties with a coloration efficiency of 58 cm(2) C-1. Large modulation of transmittance (similar to 50% at 632.8 nm) and a switching speed of about 8 s are also achieved with this macroporous film. (C) 2010 Elsevier Ltd. All rights reserved.