Self-organized macroporous tungsten trioxide (WO3) films are obtained by anodic oxidation of DC-sputtered tungsten (W) layers on 10mm×25mm indium tin oxide (ITO)-coated glass. Under optimized experimental conditions, uniformly macroporous WO3 films with a thickness of ca. 350nm are formed. The film shows a connected network with average pore size of 100nm and a pore wall thickness of approximately 30nm. The anodized film becomes transparent after annealing without significant change in macroporous structure. In 0.1M H2SO4, the macroporous WO3 films show enhanced electrochromic properties with a coloration efficiency of 58cm2 C−1. Large modulation of transmittance (∼50% at 632.8nm) and a switching speed of about 8s are also achieved with this macroporous film.