An interfacial reaction between Ni-SDC anodes and the LSGM electrolyte was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to clarify its effect on the SOFC performance. Highly resistive fine particles were formed in the vicinity of the Ni-SDC/LSGM interface as a result of the reaction between Ni and LSGM. TEM/EDX analyses revealed that these particles were MgO, which has a much lower electronic conductivity than Ni. The particles were localized on the surface of the Ni grains in the Ni-SDC anodes. The effect of MgO particle formation on the SOFC performance depended on the anode thickness. The particles significantly increased the area-specific ohmic resistance of thin anodes (less than 15 mu m), but they hardly increased the resistance of thick anodes at all. (C) 2008 Elsevier B.V. All rights reserved.