The decolorization and mineralization of Acid Red 27 (AR27), an anionic monoazo dye of acid class, was investigated using UV radiation in the presence of H2O2 in a tubular continuous-flow photoreactor as a function of oxidant concentration, reactor length, flow rate and light intensity. The removal efficiency of AR27 depends on the operational parameters and increases as the initial concentration of H2O2 and light intensity are increased but it decreases when the flow rate is increased. The AR27 degradation was followed through HPLC, UV-vis and COD analyses. The results of these analyses showed that the final outlet stream from the photoreactor was completely mineralized. The UV/H2O, process was also able to mineralize nitrogen and sulfur heteroatoms into NH4+, NO3-, NO2- and SO42- ions, respectively. The nitrogen of azo group was transformed predominantly to NH4+ ions. Decreasing the flow rate results in the reduction of COD and promotion Of SO42- at the final outlet stream of the photoreactor. (C) 2004 Elsevier B.V. All rights reserved.