Supported Co ultrafine partical catalysts were prepared by means of sol-gel methods and supercritical drying. Their catalytic performance for CO oxidation was studied. The results indicate that the catalysts have high activity even with low content (1%～2%). They show good heat stability and can be performed in a wide reaction temperature area ranging from 160℃ to 800℃ .With the increase of Co Concentration, the activity and stability of Co-SiO₂ increase.