Potentiometric sensors based on yttria stabilized zirconia (YSZ) with WO3 as sensing electrode were fabricated using either Pt or Au electrodes. The sensors were studied in the temperature range 550-700°C in the presence of different concentrations (300-1000 ppm) of NO2 and CO in air. The response to NO2 was very stable with fast response time (20-40 s). The best sensitivity (18.8 mV/decade) using Pt electrodes was observed at 600°C. At the same temperature a cross-sensitivity (-15 mV/decade) to CO gas was also noticed. The response to CO was decreased (-4 mV/decade) using Au electrode. The role played by WO3 on the sensing electrode was discussed.