The influence of different aromatics on the deep hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over a commercial NiMo/gamma-Al2O3 hydrotreating catalyst was investigated in a fixed-bed multiphase microreactor under designed conditions. Both the sulfur- containing compounds and the aromatic compounds in feeds and hydrotreated products were identified and quantified by GC-AED. Catalyst deactivation was observed, and a simple model for it was established. The kinetic behavior of these model compounds was studied with an assumption of pseudo-first-order reaction kinetics. The rate constants and the corresponding activation energies were determined, and the heat of adsorption for each compound on the catalyst surface was computed by density functional theory using the Material Studio software. The HDS rate for 4,6-DMDBT was much lower than that for DBT, which is attributed to the steric hindrance of the methyl groups at the 4 and 6 positions. The apparent activation energy of 4,6-DMDBT was higher than that of DBT under the same conditions. TThe HDS reaction rate significantly decreased with an increase of the content of aromatics in the feed. Aromatics with 2 or more rings were found to have stronger retardant effect on HDS than monoaromatics. This adverse effect was more pronounced for 4,6-DMDBT than for DBT. The competitive adsorption between the sulfur compounds and aromatics on the catalyst surface was the main reason for the decreased HDS efficiency as qualitatively verified by the heat of adsorption data.