Role of oxygen partial pressure (PO 2) on the chemical and structural stability of porous strontium doped (20 mol%) lanthanum manganite (LSM)-8 mol% yttria stabilized zirconia (YSZ) composite has been studied. LSM and YSZ powders and pore former were mixed uniformly and uniaxially pressed into pellets. The pellets were sintered at 1400 °C for 2-10 h in 0.21-10 -6 atm PO 2. Structural, chemical, and microstructural changes were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Density of the LSM-YSZ composites increased from 65% to 85% during sintering with decrease in the oxygen partial pressure. The crystal structures of LSM and YSZ maintained rhombohedral and cubic structure, respectively, under all sintering conditions. Formation of lanthanum zirconate (La 2Zr 2O 7) phase was observed in air after 10 h sintering and in 10 -3 and 10 -6 atm PO 2 after 2 h sintering. MnO x was found in 10 -6 atm PO 2 sintered composites. Lower PO 2 exposure also enhanced the grain growth. Thermal expansion coefficient (TEC) of the LSM-YSZ composites, determined by dilatometry, decreased from 11.5 × 10 -6 °C -1 for the air sintered samples to 10.3 × 10 -6°C -1 for the samples sintered in 10 -6 atm PO 2 due to the formation of La 2Zr 2O 7 phase.