Electrochemical oxidation of an azo dye (Reactive Red 120) was studied in acidic media (1 M HClO 4 ) using DSA type (Ti/IrO 2 -RuO 2 ) and boron doped diamond (BDD) anodes. Ti/IrO 2 -RuO 2 exhibited low oxidation power with high selectivity to organic intermediates and low TOC removal (10% at 25°C and 40% at 80°C). On the other hand BDD was found to be suitable for total mineralization of the organic loading to CO 2 . In both cases, the decoloration of the solution was almost 100% achieved very quickly with BDD (2 Ah L -1 ) but only after long treatment with Ti/IrO 2 -RuO 2 (25 Ah L -1 ). The instantaneous current efficiency (ICE) was up to 0.13 in the case of Ti/IrO 2 -RuO 2 and up to 0.45 in the case of BDD.