A partial oxidation test was performed using a La0.6Sr0.4Fe0.8CO0.2O3 (LSFCO6482) membrane in the surface limited conditions at a temperature range of 800-920 degrees C and in a syngas side atmosphere of CH4 diluted with Ar (100%, 25.6% and 1%) in order to investigate chemical stability and oxygen permeation properties. On the surface, deposited carbon was observed in the test and it was revealed to be graphite by an insitu Raman measurement. It was combusted by oxygen fed through the membrane. Segregation of the membrane on both surfaces was observed in all specimens after the test. Moreover, significant decomposition occurred on Air side surface of the membrane which tested in a syngas side atmosphere of 25.6% and 100%. However, the significant decomposition did not affect to be oxygen permeation properties, but it did affect its mechanical strength. (c) 2006 Elsevier B.V. All rights reserved.