Abstract Alumina supported CoMo catalysts have been synthetized by dry impregnation usingcomplexing agents in the impregnating solution. The effect of the preparation on the state and dispersion of molybdenum and cobalt in the oxidic and sulfided form was studied by various characterization techniques (UV, XPS, Raman spectroscopy, HREM). Molybdenum appears to be present as well dispersed oxomolybdenum species in the oxide form even at high loading (30 wt% MoO3). This good dispersion of molybdenum is preserved after sulfidation which induces the formation of MoS2 crystallites whose morphology has been determined by HREM. This preparation method allowed a better dispersion of the Co atom in interaction with the MoS2 crystallites. The catalytic activities were evaluated in thiophene hydrodesulfurization and the relation between the activity and the dispersion is discussed.