Fully solid state SOx sensors have been investigated with a galvanic cell of Pt, Ag/Ag-beta "-alumina/SO3, SO2, O-2, Pt using tubular Ag-beta "-alumina as solid electrolyte, metal silver as solid reference electrode, and porous Pt as working electrode. The values of electric motive force (EMF) of the sensors are consistent with the theoretically calculated ones at temperatures above 550 degrees C in the p(SOx) range of at least 10-50 000 ppm. Applying catalysts such as Pt-net and V2O5 in the gas upstream considerably improves the sensor performance and extend its working temperature down to 450 degrees C. The reproducible EMF values are obtained in the gas flow velocity of 0.2-0.4 cm/s. The response time of the sensors is 50-100 s as the p(SOx) changes. The sensors exhibit a good selectivity to SOx against hundred-fold concentrations of CO2, NO2 and H2O.