Supported thin film oxygen separation membranes are suitable for membrane reactors applications such as oxyfuel or syngas production. Porous supports provide mechanical stability to supported thin film oxygen transport membranes and to allow unrestricted gas access to membrane layer. The feedstocks for co-extrusion and co-sintering of a porous Magnesium oxide (MgO) support with a thin film of cerium gadolinium oxide (Ce0.9Gd0.1O1.95-δ, CGO) as active oxygen transport membrane layer has been developed using a thermoplastic ceramic system and graphite as pore former. The feedstocks have been optimized with respect to flow behavior, co-sintering and final layer properties. Crucial parameters, such as similar flow resistance and linear shrinkage for both materials are necessary to achieve asymmetric structure successfully. Porosity above 30% and final grain size for the MgO support is investigated by varying amounts of pore former, polymer content and different pre-calcination temperatures of the as received MgO powder. Thermal analysis (TG/DTA) and dilatometry were employed to optimize de-bindering and sintering regime in order to achieve desired support porosity and defect free structure.