Abstract: In order to improving the reliability and stability of testing, a new device for testing the isothermal adsorption/desorption property of tobacco was designed. The device was mainly composed of a gas pre-mixing unit, a thermostatic chamber, a weighing unit and a control and data acquisition unit. Gas pre-mixing unit mixed saturated moist air with dry air and produced mixed air of 5℃-90℃ and RH 5%-90%. The body of thermostatic chamber was made of metal-thermal insulator-metal plate, a PID controller regulated water temperature to maintain a constant temperature. In the weighing unit, testing chamber and weighing sensor were independently located so as to realize accurate weighing at high temperature and high humidity environment. Upper level PC software directly communicated with all components through serials to facilitate testing parameter setting, automatic regulation and real-time monitoring. The reliability and stability of the device were validated via repeated blank tests, and the adsorption/desorption of cut tobacco samples of C3F from Shandong was investigated by the device. The results showed that the device could be used to test the isothermal adsorption/desorption property of tobacco, the test process was stable, reliable, online and dynamical, the tobacco sample mass ranged from 0.0001 to 100 g, air temperature 5℃-90℃ and RH 0%-90%; the measurements featured good repeatability and could be used to characterize the moisture adsorption/desorption characteristics of tobacco samples.