Sensitive detection of ammonia (NH3) in exhaled human breath, may offer useful information for early diagnosis of kidney disease. Traditional chemical NH3 sensors usually suffer from ambient humidity. In this work, NH3 sensor operating under high humidity at 25 ℃ with enhanced response and selectivity has been achieved based on biomass hydrogel poly-l-glutamic acid and l-glutamic acid (PGA/GA). The response of the optimum PGA/GA sensor to 50 ppm NH3 at 80% relative humidity (RH) reaches 8.4, and the sensor can detect 0.5 ppm NH3. The special ionic conductive NH3 mechanism of the PGA/GA sensor was intensively studied by complex impedance plots and a quartz crystal microbalance. The high response, low detection limit, high stability and the non-toxic characteristics of biomaterials suggest PGA/GA sensors are promising for exhaled breath analyzer.