The MoO3/alumina and Mo/active carbon catalysts of various loadings were prepared by the new slurry impregnation method (SIM). The slurry of MoO3 in water was added to the support. The pH of the slurry was 2.5 and this was favourable for the adsorption of molybdate anions on alumina and active carbon with the point of zero charge 7.0 and 7.5, respectively. The low solubility of MoO3 was sufficient to transport molybdenum species from solid MoO3 to the adsorbed phase. The equilibrium was achieved after 5 weeks at 30-50 degrees C. The calcination was not necessary and was left out. This was especially advantageous for active carbon support which is susceptible to oxidative damage. The maximum loading achieved was 18 and 31 wt.-% MoO3 for Al2O3 (195 m(2) g(-1)) and active carbon (1100 m(2) g(-1)), respectively. The activity was tested in the hydrodesulfurization of thiophene at 1.6 MPa and 250-400 degrees C. The activity of the SIM samples was similar to the activity of the catalysts prepared by the conventional impregnation method (CIM) with ammonium heptamolybdate. The dependence of the activity on loading for the SIM samples was the same as reported in the literature for CIM catalysts. On alumina the activity per unit of molybdena was constant in the whole range of the loading 0-18 wt.-% MoO3. On active carbon it gradually decreased in the whole range of the loading from 0 to 31 wt.-% MoO3. It is concluded that the nature of the SIM catalysts is the same as of the CIM catalysts but the SIM possesses several advantages.