Co-doping B-site of perovskite oxide LaxSr1-xCoyFe1-yO3-delta (LSCFO) with Cr6+ and Mg2+ ions has been attempted in this research for revamping chemical stability and oxygen ionic conductivity of this mixed conducting oxide. It is known that partial substitution for B-site cations of LSCFO by Cr gives rise to a significant improvement on chemical and thermal stability of the perovskite oxide. On the basis of this doped structure, introduction of an immaterial dose of Mg2+ ion into its B-site results in a microstructure consisting of smaller grains with higher density than its precursor. Furthermore, the resulting perovskite oxide La0.19Sr0.8Fe0.69Cr0.2Mg0.01O3-delta (LSFCCMO) displays higher O2- conductivity than the solely Cr-doped LSCFO besides the improved chemical stability against reduction in 5% CH4/He stream at 850 degrees C. A detailed examination of the oxidation states of B-site transition metal ions by XPS has also been conducted as a part of structural characterizations of LSFCCMO. The assessment of relative O2- conductivity shows that the grain boundary area plays a more important role than the bulk phase in facilitating ion transport, but with comparable boundary areas the higher densification level is favorable. (C) 2009 Elsevier B.V. All rights reserved.