This work discusses the decolorization and degradation of textile azo dye solutions containing Acid Yellow 36 (AY-36) by the electro-Fenton process (EF) using an undivided electrochemical cell containing a boron doped diamond (BDD) electrode as cathode for H2O2 production. The independent parameters of current density, dye concentration, Fe2+ concentration and electrolysis time in the range of 8-23 mA/cm(2), 60-80 mg/L, 0.1-0.3 mM and 10-50 min, respectively, were evaluated. Experimental data were optimized by means of a 24 factorial design and Response Surface Methodology (RSM). These results revealed that the optimal operating conditions to achieve 95.9% efficiency for dye decolorization with complete degradation were current density = 15 mA/cm(2), AY-36 concentration = 80 mg/L, Fe2+ content = 0.3 mM and electrolysis time = 50 min. This was confirmed with UV-vis and HPLC assessments during the EF/BDD treatment. (C) 2011 Elsevier B.V. All rights reserved.