Cell damage caused by redox cycling in which the anode is electrochemically oxidized was investigated in order to detect the initial damage before cell failure. In order to prevent catastrophic destruction of the cell, partial electrochemical oxidation was used in the redox treatment and controlled at a very low degree of oxidation of the anode. As a result, the cell performance degraded because of the partial redox cycles without a decrease in open-circuit voltage, and no mechanical damage was observed in the electrolyte. However, microcracks at the interfaces between ScSZ particles and Ni particles in the anode layer in active cell area were observed. These results indicated that the microcracks in the anode layer were the initial damage caused by partial redox cycles in which the anode was electrochemically oxidized and caused the degradation of the cell performance. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3098504] All rights reserved.