BaTiO3 was synthesized by hydrolysis of Ba(iso-OC3H7)(2) and Ti(iso-OC3H7)(4) and calcination at 873 K in a N-2 atmosphere. A powder with a surface area of 42-47 m(2) g(-1) was obtained without peptization. Under a CO2 partial pressure of 10 kPa, it adsorbed 4-6 mu mol m(-2) of CO2 at 298 K and 2-3 mu mol m(-2) at 773 K. The impregnation of CuO, MgO and La2O3 did not much change the CO2 adsorption. The dynamic adsorption by gas chromatography suggested that the CO2 molecules adsorbed on the BaTiO, powder were mobile at 773 K. A clear BaTiO3 sol, synthesized with peptization, was coated onto a porous alpha-alumina support by repeating a dipping-drying-firing procedure. The separation factor of CO2 to N-2 through the membrane was 1.12-1.2, which was higher than the value of the Knudsen diffusion mechanism, 0.8.