A SOx sensor using NASICON electrolyte was developed for monitoring of air pollution. The following galvanic cell with Na₂SiO₃(Pt) reference electrode was assembled (수식) Na₂SiO₃ was used as an indicator electrode to protect NASICON electrolytes from chemical reaction with SO₂. The EMFs were measured after injecting SO₂ in the initial concentrations range of 5∼5 ppm at 400∼550℃. The measured and calculated potentials were in good agreement above 500℃. However, the cells were unstable below 500℃, most likely due to incomplete attainment of chemical equilibrium. Response time was within 10 min. Based on the stability and response time of this cell, the NASICON solid electrolyte with Na₂SiO₃(Pt) as the reference electrode and Na₂SO₃ (Pt)as the indicator electrode showed the possibility of a reliable, inexpensive commercial solid-state SO_x sensor.