We have developed a method for evaluating stress conditions in operated SOFCs based on in-situ Raman scattering spectroscopy. This method uses F 2g vibration mode of CeO 2 in interlayer of anode supported type SOFC as a probe, and we can calculate stress m an interlayer, i.e. stress in an electrolyte from the shift of a Raman peak. We apply this method to typical anode supported type cells and evaluate stress conditions during operation. Using this method, stress conditions in the electrolyte before operation is evaluated to be compressive, consistent with XRD and literature. During operation, stress conditions changed by the reduction of NiO to Ni; the compressive stress changed to tensile. In addition, the standard deviation of stresses became larger than before reoxidation, and nonreversible. These results indicate that compressive residual stress introduced into the electrolyte during fabrication process is relaxed, and suggest that an electrolyte becomes mechanically unstable during operation.