A compact tubular type sensor based on NASICON (sodium super ionic conductor) and Sm2O3 sensing electrode was developed for the detection of toluene gas. NASICON was prepared by sol–gel method. Sm₂O₃sensing electrode was used to investigate characteristics to toluene (C7H8) at various operating temperatures. The sensor using Sm₂O₃gave excellent sensing properties to 5–50 ppm C₇H₈in air at 350–450 °C. The EMF (Electromotive Force) value of the sensor was almost proportional to the logarithm ofC₇H₈concentration, the sensitivity (slope) toC₇H₈was −75 mV/decade at 430 °C. It was also seen that the sensor showed a good selectivity to C7H8 against NO₂, NO, Cl₂, SO₂, NH₃, CO and CH₄. The sensor had speedy response kinetics toC₇H₈too, the 90% response times to 5 and 50 ppm C7H8 were 45 and 35 s, respectively, and the recovery times were 8 and 60 s, respectively.