Direct feeding of biogas to SOFC, which is derived from municipal organic wastes, has been studied aiming at the development of a carbon-neutral renewable energy system. However, in the direct-feeding of biogas to a real SOFC, strong temperature gradient generated in the cell attributed to endothermic reforming reaction can cause cell fracture in the worst case. Air addition to biogas is one of the most effective ways to solve this problem. In this study optimum air amount added to biogas was evaluated in the view points of thermo-mechanical reliability, electrochemical and internal reforming efficiencies. (C) 2012 Elsevier B.V. All rights reserved.