Two series of anode supported solid oxide fuel cells (SOFC) were prepared, one with a composite cathode layer of lanthanum strontium manganite (LSM) and yttria stabilized zirconia (YSZ) on top and the other further has a LSM current collector layer on top. The fuel cells were heat treated at 1,000 °C in air or nitrogen choosing dry or humid (70% steam) conditions. XRD, SEM, and XPS investigations were performed on the various samples. The most severe modifications were observed in humid nitrogen atmosphere at low oxygen partial pressure. LSM surface change goes along with a decrease of manganese concentration and strontium enrichment on the surface of the materials. Formation of monoclinic zirconia and zirconate phases was also observed. These results give a closer insight into possible degradation mechanisms of SOFC composite cathode materials in dependence of humidity and oxygen partial pressure.