The chemical stability of the interface of lanthanum strontium iron cobalt oxides (LSCF) and lanthanum strontium magnesium gallium oxide (LSGM) was investigated. LSCF and LSGM do not coexist stably, and it makes solid solutions at higher temperatures by the fast interdiffusion of metal components. The bulk and grain boundary diffusivities were determined as a function of temperature for LSGM, LSCF, and lanthanum strontium manganite current collectors. The activation energies of bulk diffusivity of Co or Fe in LSGM or LSM, and Mn in LSCF are around 500 kJ mol(-1). The effect of grain boundary as a fast diffusion path was clearly visualized for manganese diffusion in LSCF. (c) 2006 The Electrochemical Society.