Adsorption/desorption phenomena which are reactions of adsorbing vapor with exotherm and desorbing vapor with endotherm depend on the adsorbent temperature and vapor pressure. When the pressure is constant, the amount of the adsorbed vapor increases with decreasing the adsorbent temperature generally. Adsorption/desorption rate controlled by the adsorbent temperature in constant pressure is a dominant characteristics to predict the performance of adsorption chillers and desiccant systems. It is important to measure accurately the variation in the adsorbed amount and the adsorbent temperature in transient adsorption/desorption process. Generally, gravimetric method is used to measure the adsorption/desorption rate from adsorbent weight change, because this method allows measuring that in constant pressure. Now a day, two significant methods those are thermal gravimetric analyzing method and magnetic floating balance method have applied the gravimetric method and can measure the weight change accurately. However, these methods cannot measure the adsorbent temperature directly and accurately, because the adsorbent is put on a balance and a thermo meter is put on near the adsorbent. Adsorbent temperature affects the amount of equilibrium adsorption directly. Therefore, we investigated to improve the measurement accuracy of adsorbent temperature, and then we tried to establish a measurement method on adsorption/desorption rate with a cantilever. In this novel method, an adsorbent sample and an electrical heater for controlling adsorbent temperature and thermocouple for measuring the adsorbent temperature are loaded on the tip of the cantilever. Adsorption/desorption rate is measured from difference in deflection of the cantilever caused by weight change of adsorbent with laser displacement sensor. We have already made a pretest which is measurement test of weight with this method, and confirmed that 20 mg variation of weight can be measured within 2 mg accuracy. We carried out the measurement of adsorbed vapor mass in desorption process as an example, and discussed the influence of temperature measuring point on desorption rate. Furthermore, diffusivity of water vapor in adsorbent has been discussed. Finally, we confirmed that this method can detect the mass change precisely.