This work focuses on the sensing performance of the sensor to chlorine (Cl₂) gas in air based on sodium super ionic conductor (NASICON) and oxide electrode. Among eight single oxides examined, Cr₂O₃exhibited the highest sensitivity to Cl₂gas in air at 300 °C. ΔEMF values of the sensing device attached with Cr₂O₃changed linearly with the logarithm of Cl₂concentration in the range of 5–50 ppm. The sensitivity of the sensors was testified by using Cr₂O₃electrode sintered with different temperature. The sensor using Cr₂O₃sintered at 600 °C showed the largest sensitivity to Cl₂at 300 °C. Through burying the reference electrode in middle of the NASICON layer and decreasing the area of the reference electrode, the sensitivity of the sensor to Cl₂can be greatly improved. Finally, a sensing mechanism related to the mixed potential was proposed for the sensor based on NASICON and oxide electrode.