Srbeta-alumina was synthesized in a SrO-MgO-Al2O3 system by solid state sintering, and the electrical conductivity was measured at 873-1673 K by impedance spectroscopy. The oxygen concentration cell method was applied to measure the ionic transport number. The ionic transport numbers were close to 1 in the temperature range between 1200 and 1600 K. Open- and closed-type CO2 gas sensors were constructed using the Srbeta-alumina solid electrolyte and a Pt-SrCO3 auxiliary electrode. The CO2 sensors responded well to the changes of CO2 partial pressures at temperatures of 1073-1373 K. (C) 2003 Elsevier Science B.V. All rights reserved.