Solid state electrochemical sensors using yttria-stabilized zirconia (YSZ) plate and Cr2O3-WO3 nanocomposites were fabricated. The effects of the sintering temperature on the electrode microstructure were investigated. It was found that the sensor sintered at 1000 °C exhibited larger sensitivity to NO2 in the examined range of 20–300ppm than other sensors sintered at 800 °C, 900 °C, and 1100 °C; and it was speculated that the microstructure of the SE was the primary factor. The NO2 sensing characteristics of the sensors were examined at high temperature.