The performance of an electrocoagulation process operated at a batch recirculation mode for treating petroleum refinery wastewater using aluminium as a sacrificial anode and stainless steel as a cathode was investigated. Effects of operating factors such as the applied voltage (15-30 V), flow rate (50-200 mL/min) and pH (4-10) on the chemical oxygen demand removal were investigated. Using Box-Behnken design (BBD), a mathematical model relating the essential operational parameters to chemical oxygen demand (COD) reduction was constructed . Results showed that chemical oxygen demand (COD) removal efficiency significantly increased with the increase in the applied voltage and with the increase in flow rate till the optimum value. Experimental chemical oxygen demand removal of 87.605% was attained at the optimized conditions (applied voltage=28.2 v, flow rate=200 mL/min, pH=7). Results showed that the successful of Box-Behnken design in determining the optimum condition for removal of chemical oxygen demand (COD).