The photocatalytic degradation of Reactive Black 5, a textile azo dye, has been investigated in aqueous heterogeneous solutions containing semiconductor oxides as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first kinetic order according to the Langmuir-Hinshelwood model. CO2, NO3-, and SO42- ions have been identified as mineralization products. Various commercial photocatalysts were compared with respect to their decolorization efficiency, as well as the production of CO2. The effect of pH and H2O2 on the reaction rate was ascertained.