The present paper reports on the influence of the support on the active phase in hydrodesulfurization (HDS). An Mo12S24 cluster appears to be a suitable model of the active phase fora DFT approach; it was docked to an elementary model of alumina. This study shows that the MoS2 sheet perpendicular or nearly perpendicular to the alumina surface is the stable configuration. However the creation of bonds between the active phase and the support does not modify the charge of the unsaturated molybdenum atoms considered as active sites in HDS.