Reliable real-time and in-situ monitoring of ammonia volatilization could provide invaluable information in improving agriculture ammonia fertilizer utilization efficiency and solving ammonia relevant environmental issues, however, few applicable monitoring techniques are available in the current market. This work reported a new gaseous ammonia sensing principle and developed a gas-permeable membrane-based conductivity probe (GPMCP) to obtain critical information that enables insightful understanding of agriculture ammonia volatilization process. The analytical principle based on real-time measurement of the rate of conductivity increment in the receiving solution to achieve real-time, in-situ gaseous ammonia concentration and volatilization flux in a reliable and continuous fashion. It is also capable of obtaining an average ammonia volatilization flux and amount over a deployment period. The delicate design of GPMCP and developed precalibration strategy in this study bestows this technique a direct method that can effectively avoid ongoing calibration. Field deployments results showed that GPMCP had significant advantages on presenting continuous detailed ammonia volatilization information. The reported GPMCP can be an effective tool to monitor agricultural ammonia volatilization process.