A compact tubular sensor based on NASICON (sodium super ionic conductor) and porous Cr 2 O 3 sensing electrode was designed for the detection of ammonia. The sensor gave excellent sensing properties to 50–500ppm ammonia in air at 250–450°C. The EMF value of the sensor was almost proportional to the logarithm of ammonia concentration, the sensitivity (slope) was −89mV/decade at 350°C. It was also seen that the sensor showed a good selectivity to ammonia, and an excellent resistance to water vapor. The sensor had speedy response kinetics to ammonia, the 90% response time to 50ppm ammonia was 30s, and the recovery time was 60s.