Dual-phase composite oxide 60 wt% Ce0.8Sm0.2O2 (- delta)-40 wt% SrCo0.9Nb0.1O3 (- delta) (60SDC-40SCN) which exhibits high oxygen permeability and good CO2 tolerance was developed. X-ray diffraction (XRD) patterns and dense surface topography observed by scanning electron microscopy (SEM) revealed a good compatibility of the two oxides. A high oxygen permeation flux of 1.54 mL min(-1) cm(-2) through the as-prepared dual-phase membrane (0.8 mm in thickness) was obtained under the gradient of air/He at 1223 K. In situ high-temperature X-ray diffraction demonstrated that SDC and SCN in 60SDC-40SCN membrane could retain their original phase structure from room temperature to 1223 K in CO2-containing atmosphere. The oxygen permeation fluxes of 60SDC-40SCN membrane showed a good reversibility when switching the sweep gas between CO2 and He. Comparing with single-phase SCN membrane, oxygen permeation flux of dual-phase 60SDC-40SCN membrane was more than twice when pure CO2 acted as the sweep gas, and the oxygen permeation flux could remain stable for 120 h. All the experimental results imply that dual-phase 60SDC-40SCN membrane has a great potential in oxy-fuel combustion process. (C) 2016 Elsevier B.V. All rights reserved.