Abstract: Thin films of WO3 nanoporous structure grown on tungsten substrates using the anode oxidation method were studied. The effects of anodic oxidation conditions such as the concentration of NH4F in the electrolyte， the applied voltage and the heat treatment schedule on the surface morphologies of the WO3 film were investigated. The preparation conditions to form nanoporous WO3 film with good microstructure were optimized. It was found that the films prepared in electrolyte containing 005 wt.% NH4F for 20min with the applied voltage of 60V at 20℃ exhibited the expected nanoporous morphology with self assembled nano multilayer mesh structure closely packed. In addition，after heat treated at 450℃ for 3h with a heating rate of 5℃/min， the amorphous films crystallized without changing their asobtained nanoporous structures.

Key words: WO3, anode oxidation, NH4F, nanoporous structure, heat treatment