The determination of trace moisture in clorine is a challaging task. The occurrence of water in combination with chlorine produces hydrochloric acid which is highly corrosive to system components. To analyze trace moisture in a proper way our sensor has been used for many years with excellent reliability and long term stability for measurements in chlorine gas. The parts of the sensor which comes into contact with the chlorine consist of platinum, Duranglas, and Teflon. This ensures a long life-span and a high measurement accuracy of the sensors.