Nickel-molybdenum sulfide catalysts for the hydrogenation of aromatic hydrocarbons have been prepared by the in situ decomposition of oil-soluble precursors Mo(CO)(6) and Ni(C7H15COO)(2) in a hydrocarbon feedstock and characterized by HRTEM and XPS. The resulting Ni-Mo sulfide material exhibits high catalytic activity in the naphthalene hydrogenation reaction. An optimum Mo/Ni ratio of 1/2 has been selected.