A new preparation of supported MoO3 is described. Slurry MoO3/water is used instead of the solution (NH4)(6)Mo7O24 Preparation and HDS activity are illustrated for MoO3 supported over Al2O3, active carbon and ZrO2. Another application of the new principle is the preparation of high surface area MoO3/MgO by the reaction of MgO with slurry (NH4)(6)Mo7O24/ methanol. Texture of MgO that is deteriorated in aqueous solution of (NH4)(6)Mo7O24 is stable in that slurry. "Slurry impregnation" is a special case of equilibrium adsorption impregnation. It is simple and it provides monolayer dispersion of molybdena.