Oxidation (decolorization/degradation) of Ponceau S azo-dye in aqueous solutions by electro-generated Fenton's reagent (Fe2+/H2O2) was optimized. This was carried out in a reactor containing 0.05 M Na2SO4 solution of pH 2.5 and a catalytic quantity of 0.1 mM FeSO4 while a cathode potential of -1.0 V (vs. SCE) was applied. The reactor was an undivided glass electrochemical cell with a reticulated vitreous carbon (RVC) cathode and a platinum gauze anode. Progress of oxidation of various concentrations of Ponceau S with time of electro-Fenton reaction was monitored by UV-visible absorption measurements. Mineralization of the dye solutions was examined by estimation of the chemical oxygen demand removal and HPLC analysis at various times of electro-Fenton oxidation. The complete color removal of 0.05, 0.1 and 0.3 mM Ponceau S was achieved by electro-Fenton oxidation for 30, 60 and 90 min, respectively. However, approximately 98% mineralization of 0.05, 0.1 and 0.3 mM Ponceau S was achieved due to electro-Fenton oxidation for 40, 60 and 120 min, respectively. HPLC analyses showed also that almost no aromatic compounds were remaining in the treated solutions indicating the efficiency of the electro-generated Fenton's reagent for complete decolorization and significant mineralization of the Ponceau S azo-dye in aqueous solutions. (C) 2010 Elsevier B.V. All rights reserved.