This study examines membrane synthesis, structural stability, permeation properties, and long-term permeation stability of a new dense dual-phase membrane of composition La 0.85 Ce 0.1 Ga 0.3 Fe 0.65 Al 0.05 O 3−δ (LCGFA)–carbonate for high temperature CO 2 separation. Porous ceramic supports made by sintering pressed powder at a temperature below its densification temperature resulted in a desired support with an open porosity ranging between 40 and 50%. The dual-phase membranes was prepared by direct infiltration of the ceramic supports in molten carbonate at 600°C, resulting in a four order of magnitude decrease in permeance when compared to the support. LCGFA–carbonate membranes are stable when exposed to gases ranging from gas mixtures containing N 2 and various concentrations of CO 2 to simulated syngas, and exhibit a stable long term CO 2 permeation flux of 0.025mL·min −1 ·cm −2 for more than 275h at 900°C. The CO 2 permeation results show exponential dependence to increasing system temperature as well as a linear dependence to logarithmic change in CO 2 partial pressure gradients across the membrane in the CO 2 pressure range studied.