Catalysts that can enhance the radiolytic decomposition of dibenzothiophene (DBT) in the simulated petroleum were identified. Among the tested catalysts, zirconium oxide impregnated on alumina (Zr/Al2O3) showed the highest catalytic activity in the presence of gamma-rays irradiation. The preparation condition of the catalyst was optimized. The main factors that affected the conversion efficiency of DBT were studied. The results showed that in the presence of Zr/Al2O3 catalyst when the applied radiation dose was 179 kGy, the removal efficiency of DBT was 98.9%, an increase of over 80% compared to that without catalyst. The removal efficiency was higher with the lower dose rate at the same irradiation dose. The effect of gamma-rays irradiation upon the structure of the catalyst was investigated by XRD, XPS and SEM techniques. The catalyst appeared to be stable under the gamma-rays irradiation except the surface coverage by the oxidized organic compound. In addition, the possible mechanism for the synergistic effect of gamma-rays irradiation and catalyst was proposed. (c) 2006 Elsevier B.V. All rights reserved.