Composite membranes consisting of a proton-conducting ceramic and an electronic conductor are promising in reducing the cost in the separation of hydrogen from CO2. However, the lack of a stable ceramic in CO 2 with sufficient proton conductivity remains a great hurdle. In this study, we investigated the hydrogen permeation performance and chemical stability of composite membranes based on doped ceria and Ni. Doped ceria used to be considered as a very poor proton conductor for a long time. However, our results show that ceria heavily doped with rare earth element possesses significant proton conductivity. Compared with membranes based on perovskite-type oxides, hydrogen separation membranes based on fluorite-type ceria show much higher stability in H2O and CO2. © 2010 American Chemical Society.