In this paper, two kinds of perovskite-type mixed conductor materials. Ba0.5Sr0.5Co0.8Fe0.2O3-delta and BaCo0.7Fe0.2Nb0.1O3-delta , were prepared by solid state synthesis. By combination of thermal gravimetric analysis, XRD and SEM, the high-temperature chemical stability of these two materials in pure Ar, 10% CO2+ Ar and 40% H-2 + Ar atmosphere was studied. In addition, oxygen permeation tests were also conducted in order to study the two materials' long term stability under service condition of coke oven gas (COG) partial oxidation reforming. The results show that BaCo0.7Fe0.2Nb0.1O3-delta material, in which Ba occupied all A-site and B-site is partly substituted by a small amount of Nb, has a better chemical and structural stability than Ba0.5Sr0.5Co0.8Fe0.2O3-delta at high temperature under rather high oxygen concentration gradient through the membrane. At 875 degrees C, when COG flow rate was 88 ml/min and air flow was fixed at 76.89 ml/min, oxygen permeation flux through a BaCo0.7Fe0.2Nb0.1O3-delta membrane of 1 mm in thickness reached 11.5 ml/min(1)cm(2), which could meet the industrial conditions of the COG partial oxidation reforming in industrial applications. (C) 2010 Published by Elsevier B.V