A microchanneled asymmetric dual phase composite membrane of 70 vol.% Gd0.1Ce0.9 O1.95-δ-30 vol.% La0.6Sr0.4FeO3-δ (GCO-LSF) was fabricated by a "one step" phase- inversion tape casting. The sample consists of a thin dense membrane and a porous substrate including "finger-like" microchannels. The oxygen permeation flux of the membranes with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 0.06 (STP) ml cm(-2) min(-1) for the air/He-gradient and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-gradient. Oxygen flux measurements as well as electrical conductivity relaxation indicate that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of surface catalytic layers. An increase of the oxygen flux of ca. 1.49 (STP) ml cm(-2) min(-1) at 900 ºC was observed when catalysts had been added under a low oxygen partial pressure gradient. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed in air/CO-gradient over 200 hours at 850 °C. Partial surface decomposition was observed for the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2 and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric GCO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.