The influence of anthracene, phenanthrene, fluorene, acridine and carbazole on the transformation of 4,6-dimethyldibenzothiophene on a NiMo/Al2O3 catalyst was studied. Reactivities have been evaluated under increasing concentrations of inhibitors and negative effect of some polycondensed ring aromatic compounds has been shown to be in the same order of magnitude than that of N-containing compounds. Moreover, such inhibition was proposed to be due to some partially hydrogenated molecule and conclusions relative to the practice of deep hydrodesulfurization (HDS) were drawn.