CoMo/MeO (x) (S (y) )/Al2O3 catalysts have been synthesized on supports modified with oxides (sulfides) of transition metals (Co, Ni, Mn, and Zn) using decamolybdodicobaltic heteropoly acid H-6[Co2Mo10O38H4]. A correlation between the activity of the catalysts and the ability of transition metal sulfides to accumulate molecular hydrogen has been found in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and in the hydrotreating of the diesel fraction. It has been shown that the presence on the surface of Al2O3 of sulfides (NiS (x) , CoS (x) ) capable of activating hydrogen has a positive effect on the activity of the supported catalysts. It has been found that the hydrogen spillover effect, which was studied in a range of 300-350A degrees C, contributes to an increase in the hydrogenating function of the catalyst systems.