A new SO2 gas sensor based upon interfacing two composite solid electrolytes-NASICON containing up to 40 wt.% Na2O center dot Al(2)O(3)center dot 4SiO(2) glass and Sr-beta-Al2O3 containing 3 mol % Y2O3-ZrO2 with a Na2SO4 electrode and a Pt/O-2 reference electrode has been designed and tested. In this design, both the electrodes are exposed to the same test gas thus eliminating the need for a separate reference compartment. The experimental results have shown that the measured emf of the sensor varied linearly as a function of logarithm of partial pressure Of SO2 over a concentration range of 1-1000 ppm in the temperature range of 873-1073 K. The emfs were stable and reproducible and the response time was approximately 1 min. (C) 2005 Elsevier Ltd. All rights reserved.