<p>Triclosan (TCS) has attracted much attention due to its high toxicity. Recent studies have shown that triclosan is not removed after wastewater treatment. In this paper, the degradation of TCS was investigated by catalytic ozonation process and the cytotoxicity of by-products was evaluated. Coprecipitation method was used for mesoporous graphene oxide/Fe₃O₄ nanocomposite synthesis. The catalytic activity of nanocomposite was investigated in ozonation degradation of TCS in the simulated wastewater. The influence of air flow and catalyst concentration was studied. MTT Assay was used to identify the cytotoxicity of by-products. The mesoporous nanocomposite has a specific surface area of 163.27 m²/g, total pore volume of 0.267 cm³/g and mean pore diameter of 6.54&#xa0;nm. GO/Fe₃O₄ exhibited superior catalytic activity compared to Fe₃O₄ and GO (92.63%, 88.60%, and 82.70% respectively). Catalytic ozonation with GO/Fe₃O₄ increased the apparent rate constant of TCS degradation from 0.040 to 0.197&#xa0;min⁻¹ (~ fivefold), demonstrating significantly enhanced ozone utilization efficiency. Results show that catalytic ozonation reduced the cytotoxic effects of biologically treated wastewater by 88.1–97.2%. The nanocomposite demonstrated high catalytic performance for the treatment of wastewater contaminated with TCS and could yield by-products of smaller toxicity.</p>