A modified phase inversion casting method is employed for the formation of dead-end tubular membrane shape in a single step. Ce0.9Gd0.1O1.95-δ (CGO)-Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) composites are applied as the membrane material. Performance of the membrane is optimised by adjusting the processing conditions in the fabrication process. Long finger-like channels, which were found to promote oxygen permeation flux without decrease of the membrane mechanical strength, were obtained in the dead-end tubes by adjusting the ceramic loadings of the casting slurries. Slurries with lower viscosity provided reduced resistance for the channel growth during the phase inversion in water. The performance of the dual-phase membranes with varied CGO:BSCF ratios were compared. The membranes containing more BSCF show higher oxygen permeation fluxes with helium as sweep gas. It was also verified that CGO content played an important role in enhancing the mechanical strength of the CGO-BSCF membranes.