BaCo0.7Fe0.3NbxO3-delta (BCFN, x= 0-0.2) were prepared by the conventional solid state reaction process. The crystal structure, electrical conductivity and oxygen desorption property were studied by X-ray diffraction (XRD), different thermal analysis (DTA), four-terminal direct current conductivity and oxygen temperature programmed desorption (O-2-TPD), respectively. At x = 0.08-0.20, BCFN have a cubic perovskite structure, while it exhibits the hexagonal structure for x = 0.00 and the mixed phases of cubic perovskite with trace amount of hexagonal for x= 0.05. BCFN shows good structure stability in 5%H-2 + Ar reducing atmosphere, and it is enhanced with the increased Nb-doping content. The electrical conductivity of BCFN increases with increasing temperature and decreases with the Nb substitution content for iron. BCFN exhibits a p-type semiconductor and obeys the thermally activated small polarons hopping mechanism. The oxygen fluxes increase with the working temperature and the COG flow rate, but decrease with increasing Nb content. The flux of BCFN (x= 0.08)with 1.0 mm thickness membrane reaches 25.77 ml min(-1) cm(-2) at 875 degrees C, higher than most of the reported materials. (c) 2008 Elsevier B.V. All rights reserved.