The catalytic characteristics of alumina-supported cobalt catalysts which were prepared by sol-gel method were studied by XRD, XPS, and TPR. The SCR with CH4 has been investigated over these catalysts with various cobalt content in a continuous flow reactor. It was found that loaded cobalt in Co/Al2O3 existed as Co3O4 and/or CoAl2O4 and that CoAl2O4 was formed on the external surface of particles of the catalyst. The formation of CoAl2O4 was due to the addition and mixture of cobalt solution in alumina sol. The reducibility of cobalt in Co/Al2O3 prepared by sol-gel method, however, was strongly lower than that prepared by impregnation. This result was due to the low reducibility of CoAl2O4. CH4-SCR activities of Co/Al2O3 increased with temperature regardless of cobalt content and NSR under the condition of different concentration of CH4 at constant concentration of NO, 10% of cobalt content exhibited high activity at 400℃. The activities of Co/Al2O3 decreased as NO concentration decreased at constant NSR. The activity of the Co/Al2O3–2 slightly increased with the decrease of the O2 concentration but the catalytic activities of the Co/Al2O3–5 and Co/Al2O3–7 catalyst decreased with the decrease of the O2 concentration at constant NO concentration and NSR.