An attempt has been performed to develop a selective and sensitive acetaldehyde gas sensor based on yttria stabilized zirconia (YSZ) solid electrolyte in conjunction with NiTiO₃sensing electrodes (SEs) calcined at dif ferent temperatures (800, 1000 and 1200℃). Among all the evaluated sensing devices, the sensor attached with NiTiO3-SE calcined at 1000℃was found to have a maximum sensing response value of −43 mV to 50 ppm acetaldehyde and a lower detection limit of 200 ppb at an optimal working temperature of 575℃. The response and recovery times of the sensing device to 50 ppm acetaldehyde were 10 and 26 s, respectively. The present sensor also exhibited a segmentally linear relationship between the ΔV values and the logarithm of acetaldehyde concentration in the range of 0.2–1 ppm and 1–200 ppm at 575℃and the sensitivities were −3 mV/decade and −26.5 mV/decade. Furthermore, the developed sensor had a good selectivity, reproducibility, moisture in sensitivity, as well as a high temperature stability for 20 days. On basis of the polarization-curve evaluation of the present sensor, the good agreement between the observed values and the estimated values revealed that the sensing mechanism based on mixed-potential model has been confirmed.