In this paper, the results of photocatalytic experiments were presented involving a series of Nb2O5 doped nanocrystalline/nanoporous WO3 thin films, immobilized on glass plates by the reactive magnetron sputtering method. The degradation was carried out in dyeing wastewater to investigate the effects of film structure and properties on photocatalysis. The film structure was studied by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The experimental results of photocatalytic degradation indicated that the reactivity of films decreased with increasing content of Nb2O5. The modifications of WO3 with a high content of Nb2O5 (greater than or equal to 6.6 wt.%) had been shown to have negative effects on the reactivity of the nanocrystalline/nanoporous films as a result of increased amorphous content.