Degradation mechanism of the metal-supported SOFCs with NiO-Ce0.8Sm0.2O2 delta(NiO-SDC) as anode, SDC as electrolyte, Sm0.5S0.5CoO3 (SSCo)-SDC composite as cathode was addressed with an emphasis oil metal oxidation and thermal expansion mismatch. The diagnosis was based on an improved equivalent circuit model combined with impedance, microstructure and composition analysis of the cell and cell components. The impedance diagnosis indicates that the high contact resistance is a prominent factor impeding the performance of metal-supported SOFCs at 450-600 degrees C. The observed oxide scale at the interface between metallic substrate and anode, and, the weak bonding between the electrolyte and the cathode may be responsible for the high contact resistances. Energy-dispersive X-ray spectroscopy (EDX) was applied to analyze the change of surface composition of metallic substrate joined with anode in order to elucidate the formed oxide scale. In addition, based on the improved equivalent circuit model, internal shorting current of the cell due to electronic conduction was evaluated. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.