Reduction of chemical oxygen demand (COD) value of petrochemical industry wastewater (COD similar to 11 500 mg/L) by Fenton's oxidation has been investigated. Batch tests were conducted on the effluent samples to determine the optimum process conditions. Fenton's oxidation process was found to effectively reduce the COD by 97.5% in 100 min. Effects of different process parameters: pH, H2O2 dosage, Fe2+ dosage, H2O2/Fe2+ ratio, temperature were investigated. The optimum conditions were at pH 3, H2O2 concentration 3M, Fe2+ concentration 0.06M and temperature 30 degrees C. Optimum molar ratio [H2O2/Fe2+] was 50:1. At optimum conditions, 97.5% COD reduction was achieved for the typical effluent sample from nearby industry manufacturing mainly PET resins.