Naphthalenesulfonic compounds are widely used, mainly by the textile industry in the synthesis of azoic colorants. The presence of the sulfonic group is known to endow these compounds with high water-solubility and low biodegradability, although its influence on their genotoxic activity is unknown. The use of energetic oxidants is recommended for the degradation of organic compounds which are refractory to biological treatment. Ozone and ozone/activated carbon have been proposed as the best alternatives to remove these compounds. The results showed that the more sulfonic groups there are on the aromatic ring of this family of contaminants, the lower is their genotoxic activity. All the compounds studied presented genotoxic activity at elevated concentrations. Ames test results indicate that DNA damage was produced by substitution of nitrogenated bases. The system based on the combined use of ozone and activated carbon was the most efficacious in the depuration of water containing these contaminants. This approach rapidly degraded the naphthalenesulfonic acids, eliminated their genotoxic activity and reduced their organic material content using low doses of ozone.