Abstract CoO–MoO 3 /MgO and NiO–MoO 3 /MgO catalysts were prepared from MoO 3 /MgO by impregnation with methanol solutions of Co nitrate and Ni nitrate, respectively, followed by calcination at 350°C. The texture of the starting MoO 3 /MgO was preserved during this preparation. The hydrodesulfurization activity of the presulfided catalysts was evaluated using the reaction of benzothiophene (1.6 MPa, 300–360°C). Commercial CoMo/Al 2 O 3 (Shell 344) and NiMo/Al 2 O 3 (Shell 324) catalysts were used as reference points of activity. A strong synergistic effects in activity between Co(Ni) and Mo in Co(Ni)Mo/MgO catalysts was observed with an optimum Co(Ni)O content of about 3–4 wt%. The most active Co(Ni)Mo/MgO catalysts were 1.5 to 2.3 times more active than their corresponding Al 2 O 3 -supported counterparts. MgO should be considered a new promising support for Co(Ni)Mo sulfide catalysts. However, its sensitivity to water and propensity to form solid solutions with CoO and NiO must be taken into consideration in catalyst preparation.