Owing to its extensive use and intrinsic toxicity, NH 3 detection is very crucial. Moisture can cause significant interference in the performance of sensors, and detecting NH 3 in high humidity is still a challenge. In this work, a humidity-activated NH 3 sensor was prepared by urocanic acid (URA) modifying poly (ethylene glycol) diacrylate (PEGDA) via a thiol-ene click cross-linking reaction. The optimized sensor achieved a response of 70% to 50 ppm NH 3 at 80% RH, with a response time of 105.6 s and a recovery time of 346.8 s. The sensor was improved for response and recovery speed. In addition, the prepared sensor showed excellent selectivity to NH 3 in high-humidity environments, making it suitable for use in some areas with high humidity all the year round or in high-humidity areas such as the detection of respiratory gas. A detailed investigation of the humidity-activated NH 3-sensing mechanism was conducted using complex impedance plot (CIP) measurements.