Abstract: A miniaturized multilayer 3D micro/nano ammonia sensor chip is designed and prepared. An ammonia nitrogen measurement system utilizing such a miniaturized sensor chip is constructed. The method of ammonia nitrogen measurement using a miniaturized amperometric ammonia sensor is investigated. The sensor chip is fabricated by micro/nano fabrication technology. Polymer adhesive bonding method is used to achieve the encapsulation of multilayers of the sensor under relatively low temperature condition. Nanoparticles of iridium which possessses excellent electrocatalysis is utilized to enhance the sensitivity. The stability of micro Ag/AgCl reference electrode is evaluated. Measurement of ammonia nitrogen using the self-designed measurement system is presented. The characterizations of the sensor, including relationship between response and sample concentrations, response times, reproducibility and selectivity are demonstrated. A linear calibration curve between 0.5~10 mg/L is obtained with the sensitivity of 1.62 A/(mg/L) and the correlation coefficients of 0.995. The Relative Standard Deviation (RSD) is 5.73%. Meanwhile, the results reveal that the sensor possesses good selectivity.