Information on the degree of deactivation is very important for predicting catalyst life, from which the catalyst design could be further improved. The CoMo/Al2O3 catalysts, used for the hydrodesulfurization of light oil, are known to have a commercial operation time of around two years. Our goal was to establish the accelerated pre-coking conditions for obtaining a desired degree of deactivation for CoMo/Al2O3 catalysts. The effect of coking temperature on the catalytic activity for thiophene hydrodesulfurization was investigated for three coke precursors. Pre-coking with heavier precursors resulted in higher coke content and higher aromaticity as expected, i.e., in order of anthracene>naphthalene>cyclohexene. It is suggested that the established conditions of precoking for the commercial catalysts could provide a quantitive reference for evaluating the lifetime of any commercial catalysts.