A new slurry impregnation method (SIM) of the preparation of a catalyst or catalyst precursor MoO3/Al2O3 is described. Aqueous slurry of powdered MoO3 is mixed with alumina extrudates and the mixture is refluxed. A low solubility of MoO3 is sufficient for transport of MoO3 from powder form via solution to the surface of the support. The catalysts were tested by hydrodesulfurization of thiophene at 1.6 MPa and 280-400-degrees-C. Their activity was similar to the activity of industrial and laboratory MoO3/Al2O3 samples prepared by conventional impregnation with solution of ammonium heptamolybdate. The advantage of the SIM method is that calcination, producing nitrogeneous waste gases, is not required and that all deposited molybdenum species are adsorbed and not precipitated.