The oxidative degradation of an azo dye, Acid Red1 (AR1), in aqueous solution using Advanced Oxidation Processes (AOPs), has been investigated. The fast reaction kinetics and the details on the short-lived intermediate radicals from the reaction of hydroxyl radicals ((OH)-O-center dot) with AR1 were investigated by pulse radiolysis technique. Three selected AOPs such as Fenton and photo Fenton reactions, ferric perchlorate (FPC) photolysis and H2O2 photolysis, are found to be successful in the complete decolorization within a short time of treatment. The decolorization is understood as a result of destruction of the most reactive conjugated electronic position having -C-N=N-C- bridge. A considerable amount of TOC reduction is also observed using these methodologies. A second order rate constant of 3.9 x 10(9) dm(3) mol(-1) s(-1) is determined for the reaction of (OH)-O-center dot with AR1 by pulse radiolysis. The transient absorption spectra obtained from the reaction of (OH)-O-center dot is different from the reaction of the specific one electron oxidants such as N-3(center dot), SO4 center dot- and O center dot- center dot (OH)-O-center dot reacts with the dye by addition to form (OH)-O-center dot-adducts with aromatic ring as well as with the azo bond. Other oxidizing radicals undergo electron transfer to form the corresponding naphthoxyl type radical. Some of the stable intermediate products were identified by LC-Q-TOF-MS. These products are the result of hydroxylation of azo bond and ring cleavage. A plausible reaction mechanism for the degradation is elucidated from these results. The significant decolorization and mineralization demonstrate the potential application of these methodologies for the treatment of azo dyes containing effluents. (C) 2014 Elsevier B.V. All rights reserved.