In this work, conductive-diamond electrochemical oxidation of synthetic wastes polluted with azoic dyes is studied. Results show that this advanced oxidation process is able to complete the treatment of wastes polluted with large molecules such as the dyes studied in this work. The oxidation process starts with the breakage of the azoic group, and according to the changes in the total organic carbon and chemical oxygen demand observed during the electrolyses, it deals with the accumulation of carboxylic acids in the final stages of the treatment. Negligible amounts of refractory organic matter are found in the effluent of highly loaded waste treatment. The efficiency of the conductive- diamond electrolyses of azoic dyes does not seem to depend on the molecule of the dye oxidized but only on its concentration range. From the experimental results it seems that the primary mechanisms in the oxidation of dyes are the mediated electrooxidation by hydroxyl radicals and persulfate ( highly loaded wastes) and by persulfate ( diluted wastes).