4,6-Dimethyldibenzothiophene (4,6-DMDBT), one of the most refractory sulfur compounds in gas oil, was desulfurized in n-decane using NiMo sulfide supported on active carbons (NiMo/C) with a microautoclave installed with a sampling apparatus, to establish the hydrodesulfurization (HDS) kinetics and mechanism. The NiMo/C catalysts exhibited the higher activity for the HDS of 4,6-DMDBT at relatively higher temperatures of 340-380 degrees C than a commercial NiMo/alumina catalyst regardless of the carbon supports. The main route was the direct desulfurization in this temperature range. The main reaction at 300 degrees C was found to be the hydrogenative desulfurization route over the same catalyst, producing 3-(3'-methyl cyclohexyl)toluene. The direct desulfurization was significantly inhibited by the coexisting H2S regardless of reaction temperatures, although the hydrogenation route was found to be enhanced by H2S to some extent. The present desulfurization network was established by the computation curve fitting through measuring the equilibrium between 4,6-DMDBT and its tetrahydroderivative.