The influence of H2S partial pressure over the catalytic activity of MoS2, supported on three different oxides : Al2O3, TiO2 and ZrO2, was studied in the hydrodesulfurization of dibenzothiophene (DBT). A complex inhibiting effect is observed and two orders of reaction relative to H2S were determined : -1/2 and 0, as a function of H2S partial pressure. The experimental results are in good agreement with the kinetic models whereby the DBT transformation takes place through a dihydrogenated intermediate (DH-DBT). The associated mechanism considers that the heterolytic dissociative adsorption of H-2 and H2S occurs over an unsaturated Mo ion and over a stable sulfur ion.