Unsupported ceria membranes were prepared from three different cerium oxide sols (commercial sot, cerous so] and ceric sot). XRD data show that the ceria membranes derived from all sols after drying at room temperature or calcination at a high temperature exhibit fluorite type structure. The final calcined product from all ceria sols is Ce4+ oxide compound. Ceria samples derived from commercial sot contain fairly dense particles with a very low surface area, and those derived from cerous and ceric sols give very high surface area with desired pore structure as mesoporous membranes. Cerous so] is however stable at very low concentration and is ineffective to use for making supported ceria membrane. Ceric sot is stable at high concentration (around I M) and provides unsupported ceria membranes with desired pore structure. Micron-thick ceria films could be coated on macroporous alpha-alumina support with the high concentration ceric sot after the support was chemically treated sequentially with a hot acid and base. The supported ceria membranes are crack-free and pinhole-free, and exhibit fluorite type structure. Compared to a similar sol-gel derived mesoporous zirconia membrane, the supported mesoporous ceria membrane has similar pore size (about 3.2 nm), smaller tortuosity factor (2.7) and larger porosity (54%). (c) 2005 Elsevier B.V. All rights reserved.