A series of La0.15Sr0.85FeO3-delta-xLa(0.15)Ce(0.85)O(2-delta) (LSFO-xLDC) and Cu-doped LSFO-70La(0.15)Ce(0.8)Cu(0.05)O(2-delta) (LSFO-70LDCC) dual-phase membranes were prepared by one-pot method and evaluated systematically as high CO2-tolerant oxygen separation membranes. The results reveal that the stability of the membranes is improved by compositing LDC. Among the studied compositions, the LSFO-70LDC compound shows excellent stability under reducing atmosphere and CO2-containing atmosphere. The oxygen permeability of LSFO-70LDC membrane with 0.6 mm thickness is 0.49 mL cm(-2) min(-1) at 950 degrees C. In addition, LSFO-70LDC shows outstanding long-term stability with stable oxygen permeability of 0.30 mL cm(-2) min(-1) at 900 degrees C for 100 h. Cu-substitution prominently enhances the oxygen permeation performance of the LSFO-70LDCC dual-phase membrane, which delivers an enhanced oxygen permeability of 0.65 mL cm(-2) min(-1) at 950 degrees C. Moreover, the LSFO-70LDCC membrane exhibits excellent long-term stability for 100 h at 900 degrees C in both pure He and CO2. These results indicate that the developed LSFO-70LDC and LSFO-70LDCC dual-phase membranes are very promising membranes for oxygen separation.