Abstract Hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene over a synthesized nanosize-MoS 2 catalyst were investigated in a batch reactor. The catalytic activity in hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene increased remarkably with H 2 S being remained in the reaction zone. The HDS reactions of the two substrates over the present catalyst were found to proceed via a network where direct desulfurization and hydrogenation routes are essentially involved. The product contribution from the hydrogenation route is much more pronounced. Isomerized components were also identified. Dibenzothiophene and 4,6-dimethyldibenzothiophene exhibited almost identical results in terms of the reactivity and selectivity. The increase in the catalytic activity with H 2 S is probably due to the increase in the number of the potentially active sites modified by H 2 S. The kinetic investigation of the hydrodesulfurization reactions revealed the autocatalysis-like phenomena attributed to the potentially modified active sites by self-produced H 2 S. TEM image reveals that the synthesized MoS 2 may consist of a bent and/or a closed round layers which might play an important role in such autocatalysis behaviors of H 2 S in the hydrodesulfurization of polyaromatic thiophenes.