La1-xSrxCo1-yFeyO3-delta perovskite-type oxides are typical of mixed-conducting ceramic membrane materials with very high oxygen semipermeability. In this study, several different synthesis methods were compared for the preparation of La0.8Sr0.2Co0.6Fe0.4O3-delta (LSCF) powders. The coprecipitation method was found most suitable for preparation of the LSCF powder in terms of processibility into dense ceramic membranes. The oxygen permeation flux through 1.85 mm LSCF membrane exposed to O-2/N-2 mixture and helium is about 1x10(-7) mol/cm(2) s at 950 degrees C. The oxygen permeation flux increases sharply around 825 degrees C due to an order-disorder transition of the oxygen vacancies in the membrane. Oxidative coupling of methane (OCM) was performed in the LSCF membrane reactor with one membrane surface exposed to O-2/N-2 mixture stream and other to CH4/He mixture stream. At temperatures higher than 850 degrees C, high C-2 selectivity (70-90%) and yield (10-18%) were achieved with a feed ratio (He/CH4) of 40-90. The C-2 selectivity dropped dramatically to less than 40% as the He/CH4 ratio decreased to 20, The surface catalytic properties for OCM of LSCF membranes strongly depend on the oxygen activity of the membrane surface exposed to methane stream.