The H2O2/pyridine/Cu (II) advanced oxidation system is a treatment method involving a combination of a transition metal ion with ligand molecules which decomposes H2O2 to produce hydroxyl radicals (OH*), which will then lead to the mineralization of organic compounds to produce CO2 and H2O. Most researches using this system reported reduction in color only, without considering the Chemical Oxygen Demand (COD) content. This study was carried out to assess and to optimize the treatment efficiency of this system in reducing the COD of a reactive dye wastewater. Reactive dye was chosen in this study because it is the most widely used dyes in the textile industries. Full factorial design and central composite design (CCD) from the response surface methodology (RSM) were utilized in the screening and optimization of the system. Results obtained indicated that the treatment efficiency was pH independent, and this system was found to be capable in reducing the concentration of COD of the wastewater up to 73% at the optimal concentrations of 0.059 M H2O2, 0.087 M pyridine, and 0.017 M Cu (II). (C) 2011 Elsevier B.V. All rights reserved.