Residual thermal stresses in the electrolyte of the anode-supported planar solid oxide fuel cells (SOFCs) were estimated experimentally and numerically. The X-ray diffraction method was employed to measure the residual stress in the cell. To estimate the residual stress precisely, a synchrotron radiation was used as the best means of X-ray source. The wavelength of the radiation beam used for the stress measurements was 0.154 nm, and the diffraction peak of YSZ (531) plane was used for the stress measurement. The estimated residual stresses in the electrolyte were compressive stresses of around 650 MPa at room temperature. Numerical calculation for the residual stress was also carried out. (C) 2004 Elsevier B.V. All rights reserved.