Carbon dioxide-selective facilitated transport membranes containing both mobile and fixed carriers in the sulfonated polybenzimidazole copolymer matrix were successfully synthesized. Transport properties of the membranes, including CO2/H-2 selectivity, CO2 permeability, and CO2 permeance, were studied at the feed pressure of 30 psia with a feed gas stream consisting of hydrogen, carbon dioxide, and nitrogen. The effects of water content, temperature, and membrane composition on transport properties were investigated. The results showed that the increase of water contents on both the feed side and the permeate side increased the membrane performance, and the optimal operating temperature of the membranes was 100 degrees C. The membrane with an optimized composition showed a CO2/H-2 Selectivity as high as 64.9 and a CO2 permeability as high as 2539 barrers, which is very desirable in synthesis gas purification for fuel cell applications. Moreover, the membranes also have great potential in CO2/N-2 and CO2/CH4 separations for flue gas CO2 capture and natural gas purification.