Electrochemical oxidation of an azo dye (Reactive Red 120) was studied in acidic media (1 M HClO4) using DSA type (Ti/IrO2-RuO2) and boron doped diamond (BDD) anodes. Ti/IrO2-RuO2 exhibited low oxidation power with high selectivity to organic intermediates and low TOC removal (10% at 25 A degrees C and 40% at 80 A degrees C). On the other hand BDD was found to be suitable for total mineralization of the organic loading to CO2. 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/IrO2-RuO2 (25 Ah L-1). The instantaneous current efficiency (ICE) was up to 0.13 in the case of Ti/IrO2-RuO2 and up to 0.45 in the case of BDD.