A compact tubular sensor based on NASICON (sodium super ionic conductor) and CaMg₃(SiO3)₄(Asbestos, acid washed A.R)-doped CdS sensing electrode was prepared for the detection of chlorine. The sensing properties strongly depended on the sintered temperature of the sensing electrode materials. The sensor using CaMg₃(SiO3)₄-doped CdS sintered at 600 degrees C gave excellent sensing properties to 1-10 ppm chlorine in air at 100-250°C. The sensitivity (slope) was 392 mV/decade at 200 °C. And it showed a good selectivity to Cl-2 against H₂S, SO₂, NO₂, NH₃, CH₄and CO. Also it had speedy response kinetics to chlorine, the 90% response or 90% recovery time to 5 ppm chlorine was 20 s or 37 s, respectively. The phase compositions and grain size of NASICON andCaMg₃(SiO3)₄-doped CdS were examined by means of X-ray diffraction (XRD). On the basis of XPS analysis for Cl-2-absorbed sensing electrode, a sensing mechanism involved the mixed potential at the sensing electrode was proposed.