The low biodegradability of polyphenolic compounds typically found in olive processing indicated that biological treatment is not always successful in the treatment of olive oil mill wastewater in term of COD removal. In this study the results of investigations on the applicability of Fentons reagent in the treatment of this effluent were discussed. The efficiency of this method was determined. 86 % of removal COD was obtained using 5 mol H2O2 and 0.4 mol Fe2+ per liter of crude OMW. The main parameters that govern the complex reactive system, i.e., time, pH, [H2O2] and [Fe(II)] have been studied.