A solid electrolyte-type SO2 gas sensor was fabricated by the combination of the tetravalent Zr4+-conducting Zr39/40TaP2.9W0.1O12 and the O2--conducting (ZrO2)(0.92)(Y2O3)(0.08) solid electrolytes with the 0.6La(2)O(2)SO(4)-0.4Li(2)SO(4) auxiliary sensing electrode. Since the present sensor showed a continuous, quantitative, and reproducible response, which obeys the theoretical Nernst relationship, over a month, it is expected to be a suitable candidate as a practical SO2 gas-monitoring tool.