Abstract: Through the impregnation of Mo/AC catalyst with an aqueous solution of ammonium thiosulfate (ATS), the ex-situ presulfided Mo/AC-ATS catalyst was prepared; the influence of activation temperature and time on the catalytic performance in the hydrodesulfurization (HDS) of thiophene as a probe reaction was investigated. The result indicated that under the optimized activation conditions, viz., 300 ℃ and 0.5 h, the conversions of thiophene over the presulfided Mo/AC-ATS catalyst are 34% and 42% higher than those obtained over the Mo/AC catalysts sulfided with traditional DMDS and CS₂ sulfiding agents, respectively. The XPS, TPR-MS and TEM results demonstrated that the presulfided Mo/AC-ATS has a high content of Mo⁴⁺, which may contribute to its high activity in HDS.