Catalysts containing 20 wt.% Co3O4 supported on γ-Al2O3 and MgO were prepared. The catalyst precursors were analyzed by TG, DTG and DTA, and the calcined catalysts (400-700 °C) were characterized by XRD. The amount of excess surface oxygen for the catalysts was estimated iodometrically. The vapour-phase decomposition of isopropyl alcohol over these catalysts was studied. Co3O4/γ-Al2O3 catalysts are selective towards propene formation, whereas Co3O4/MgO catalysts are selective towards acetone formation. The poisoning effect of Co3O4 on both supports and the activity of the catalysts is discussed.