In this work, the decolorization of C.I. Acid Blue 25 (AB25), a commercially important anthraquinonic dye, by direct UV irradiation alone and UV/H2O2 and UV/Fe(II) processes was investigated. Experiments were conducted in batch mode using a low-pressure mercury lamp emitting mainly at 253.7 nm. For direct UV photolysis, the decolorization rate increased with decreasing pH and initial dye concentration. The decolorization of AB25 was investigated using UV irradiation in the presence of H2O2 as function of hydrogen peroxide concentration, dye concentration and pH. Additionally, the effect of salts on the bleaching of this dye was also studied. Decolorization rate was increased in the presence of UV/H2O2 compared to UV irradiation alone. The results showed that the bleaching increases as the initial H2O2 concentration increased up to a certain limit at which hydrogen peroxide reduced the bleaching by scavenging the OH radicals. The bleaching of AB25 decreased when the dye concentration increased. Decolorization rate by means of Fe(II) homogeneous photocatalysis under UV irradiation was increased compared to direct UV irradiation alone. The best working condition was found for an initial Fe(II) concentration of 30 mg L-1. The results revealed that the tested advanced oxidation processes are very effective for the decolorization of AB25 in aqueous solutions. (C) 2010 Elsevier B.V. All rights reserved.