This work describes the application of Fenton's reagent (H2O2/Fe2+) to the removal of chemical oxygen demand (COD) from olive mill wastewater (OMW) in a laboratory-scale batch reactor. The effect of different operational conditions, namely, hydrogen peroxide and ferrous ion concentrations, temperature and initial pH were evaluated. ORP, pH and dissolved oxygen were on-line monitored. Working with an initial pH equal to 3.5, a temperature of 30 degrees C, a molar ratio H2O2/Fe2+ = 15 and a weight ratio R = H2O2/COD = 1.75 makes possible a COD conversion of 70%. A kinetic study was carried out using a modified pseudo-first-order model. The experiments performed at different temperatures allowed the calculation of the Arrhenius equation parameters and the global activation energy for the pseudo-first-order reaction (28.2 kJ/mol). (C) 2009 Elsevier B.V. All rights reserved.