A solid-state electrochemical sensor for measuring SOX in a gas mixture has been designed by incorporating Na3Zr2Si2PO12, (Nasicon) and (8 mol% Y2O3)-ZrO2 (YSZ) as a solid electrolyte couple. The solid electrolyte couple consisted of 2-mm-thick sintered disk of Na3Zr2Si2PO12, and a thin film of (8 mol% Y2O3) ZrO2 approximately 6 mum thick. YSZ thin film on Nasicon disk was prepared by multiple radio frequency (RE) magnetron sputtering technique. The sensor employs Na2SO4 as an auxiliary or sensing electrode that is in contact with Nasicon. The SO2 present in the gas mixture is converted to SO3 by passing over heated Pt-catalyst. The sensor has been successfully tested in the laboratory environment. At a fixed concentration of 1000 ppm SO2, the electromotive force (emf) of the sensor was found to vary nonlinearly as a function of temperature between 823 and 1123 K. However, at a fixed temperature of 973 and 1023 K, the measured emf of the sensor was found to vary linearly as a function of the logarithm of concentration of SOX in the gas mixture between 100 and 3000 ppm. In the current sensor design, both electrodes are exposed to the same test gas eliminating the need for isolating the electrode compartments. (C) 2003 Elsevier B.V. All rights reserved.