Abstract: The influence of indole on the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and the influence of DBT on the hydrodenitrogenation (HDN) of indole were investigated over a presulfided NiMoS/γ-Al2O3 catalyst in a fixedbed highpressure microreactor. A significant negative effect of indole on the HDS of DBT was observed. The inhibitory effect of indole on the hydrogenation route (HYD) was stronger than on the direct desulfurization route (DDS). Indole and its HDN intermediate products suppressed HDS of DBT through the competitive adsorption on active sites of the catalyst. DBT and H2S produced insitu promoted the conversion of coordinatively unsaturated sites (CUS) to Brnsted acid sites on the catalyst surface, which in turn facilitated the cleavage of C(sp3)—N bond in indoline; the conversion of indole and the relative concentration of o-ethylanline (OEA) then increased. Although the presence of sulfur atoms is essential for the formation of active sites on the catalyst for HDN, a small amount of sulfur species is sufficient to maintain the HDN active sites; higher content of sulfides may bring on a negative influence on the HDN of indole.