A new sensor based on cataluminescence (CTL) produced on the surface of nanosized TiW3Cr2O14 was demonstrated for direct determination of ammonia in air. Trace ammonia was firstly absorbed on active carbon at room temperature to concentrate, then desorbed at 105°C to determine. The sensor showed high selectivity to ammonia at wavelength of 540 nm, satisfying activity at temperature of 275°C and good stability at air carrier flow rate of 115 ml/min. The linear range of CTL intensity versus concentration of ammonia was 1.0~50 mg/m3 (γ=0.9990), and the detection limit (3σ) was 0.5 mg/m3. The recovery of artificial sample was 97.45%—102.73% by this method. There was no response to benzene, SO2, CO and formaldehyde, and insignificant response to ethanol. This gas sensor allows on-line monitoring of ammonia in air.