Heterogeneous photocatalysis is a significant green technology for application in water purification. The application of Nb2O5 catalyst for the photodegradation of contaminants is few reported in the literature. Thus, the Nb2O5 catalyst was characterized by SEM, FTIR, surface area and charge surface density. This catalyst was applied to degrade indigo carmine dye, which was compared with degradation catalyzed by TiO2 and ZnO. Almost 100% of dye degradation occurred at 20, 45 and 90 min for TiO2, ZnO and Nb2O5, respectively. The effect of Nb2O5 catalyst concentration. pH and ionic strength (mu) was investigated. The Nb2O5 activity increased at 0.7 g/L and for higher catalyst concentrations the degradation was kept constant. Degradation of indigo carmine dye catalyzed by Nb2O5 was improved at pH < 4.0 and mu = 0.05 mol/L. TiO2, ZnO and Nb2O5 were recovered and re-applied in other nine reaction cycles. While TiO2 and ZnO have an abrupt loss of their catalytic activity, Nb2O5 maintained 85% of catalytic activity after 10 reaction cycles. (C) 2008 Elsevier B.V. All rights reserved.