This study was performed to investigate the variables that influence the efficiency of color removal from a solution containing an azo dye (C.I. Reactive Black 5, abbreviated here as RB5) by the combination of ozonation and electrocoagulation at iron electrodes. Several working parameters, such as initial pH, initial dye concentration, current density, salt (K2SO4) concentration, temperature, ozone flow rate and distance between the electrodes, were studied in an attempt to achieve higher color removal efficiency. The experimental results reveal that the color of RB5 in the aqueous phase was removed effectively. Under the conditions of an initial dye concentration of 100 mg/L, initial pH of 5.5, current density of 10 mA/cm(2), salt concentration of 5000 mg/L, temperature of 20 degrees C, ozone flow rate of 20 mL/min (ozone dose 0.20 g/h), and interelectrode distance of 1 cm, the color-removal efficiency reached 94%, corresponding to a reduction in COD of more than 60%. The energy consumption of the technique was approximately 33 kWh/kg of COD removal.