(Ba0.5Sr0.5)(1-x),Co0.8Fe0.2O3-delta (BSCF) (x= 0-0.3) oxides were prepared by a combined EDTA-citrate complexing method. The crystal structure' electrical conductivity, sintering behavior and oxygen desorption property of the oxides were studied by X-ray diffraction (XRD), four-probe direct current (DC) conductivity, environmental scanning electron microscopy (ESEM) and oxygen temperature-programmed desorption (O-2-TPD) technologies, respectively. At x = 0.0-0.15, BSCF had a cubic perovskite structure, the lattice parameter and electrical conductivity both decreased steadily with increasing A-site deficiency. The A-site deficiency resulted in the increasing oxygen vacancy concentration in the lattice structure and improved the sintering of the oxides. BSCF (x = 0.03) showed the highest oxygen permeability with the flux reaching 3.5 x 10(-6) Mol cm(-2) s(-1) [STP: standard temperature and pressure] at 900 degrees C through a 1.0 mm thickness membrane. Long-term stability test of BSCF (x = 0.03) membrane at 850 degrees C indicated a slight deterioration of the permeation flux, which was attributed in part to the increased A-site deficiency of the bulk from Ba2+ and Sr2+ segregation over the membrane surface. (c) 2007 Elsevier B.V. All rights reserved.