Samarium doped ceria (SDC) carbonate dual-phase membranes are permselective to carbon dioxide. This paper reports a method to prepare thin SDC carbonate membranes on an adequate base support to improve CO2 permeance of the membranes. It was found that macroporous support made of a physical mixture of SDC and 40 vol % bismuth-yttrium-samarium oxide (BYS) has the desired pore structure, ionic conductivity, carbonate nonwettability, and mechanical compatibility with the thin SDC carbonate membrane layer. Asymmetric porous supports consisting of a thin, porous SDC top layer on an SDC BYS base were prepared by the copressing method. The porous SDC top layer was filled with molten carbonate by the direct infiltration method. The final membranes consist of a 150 mu m, hermetic SDC carbonate layer on the macroporos SDC-BYS base support. The thin SDC carbonate dual-phase membrane offers significantly improved CO2 permeance as compared to thick SDC carbonate membranes. Both membrane thickness and the structure of the SDC phase affect CO2 permeance. The thin SDC-carbonate membranes exhibit CO2 flux of 1.33 x 10(-3)-6.55 x 10(-3) molts/m(2) at 550-700 degrees C, with steady state operation for at least 160 h. The CO2 permeation flux is related to upstream and downstream CO2 partial pressures by a power law, consistent with the theoretical model.