Sr-doped lanthanum cuprate was recently investigated as a potential cathode material for the intermediate temperature solid oxide fuel cell using yittria-stabilized zirconia as an electrolyte. The material thermal stability of cathode material against an electrolyte at an operating temperature plays an important role in the fuel cell's performance. In this study, the structural stability between Sr-doped lanthanum cuprate and 8 mol% yittria-stabilized zirconia was investigated by using the powder mixture and diffusion couple. The chemical reaction between these two materials in the temperature ranging from 800 degrees to 1000 degrees C was examined by X-ray diffraction analyses. The interfacial reaction behavior between electrode and electrolyte pellets of the reaction couple was examined by a grazing X-ray diffractometer, wavelength-dispersive X-ray analysis, and an electron probe microanalyzer. No reaction products were observed as these two materials co-fired at 800 degrees C. The reaction products of pyrochlore La2Zr2O7 and perovskite SrZrO3 were formed when the specimens were heat treated at over 900 degrees C. Because of the formation of these reaction products, the CuO was precipitated. Furthermore, an excess of SrZrO3 formation leads to the phase decomposition of perovskite Sr-doped lanthanum cuprate to La2-xSrxCuO4 and CuO due to a decrease in strontium concentration in Sr-doped lanthanum cuprate.