La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2 may be used as cathode and electrolyte materials, respectively, in solid oxide fuel cells. One of the requirements of the cathode-electrolyte interface is that high impedance phases are not formed at the interface during manufacture or operation of the SOFC. The interfaces of interest were prepared as a diffusion couple and by sintered powder mixtures of La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2. The structures at the interfaces were examined by transmission electron microscopy. Chemical analyses were made by energy dispersive X-ray spectroscopy. A Zr, La-based pyrochlore-type crystalline phase has been observed at some of the interfaces between La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2. In the present paper, changes in element ratios are used to obtain knowledge on how the elements diffuse with respect to each other at the interface. It was found that the formation of pyrochlore depends on the content of Mn in the La0.85Sr0.15MnO3 and on the ratio between La0.85Sr0.15MnO3 and Y2O3-stabilized ZrO2.