The present paper has dealt with the transient adsorption characteristics of the organic powder type adsorbent in a fluidized bed. The organic powder type adsorbent was made from the bridged complex of sodium polyacrylate and its diameter ranged from 30 µm to 48 µm. The measured results of adsorption isotherm equilibrium revealed that the mass ratio of the present organic adsorbent adsorbed water-vapor to the adsorbent dried were 1.3 to 2.3 times larger than that of silica gel adsorbent in the relative air humidity range from 3 to 80%. The humid air was used as a working fluid for transient experiments. The test organic powder type adsorbent was fluidized in a rectangular vessel by flowing the air from its bottom. The adsorption rate of water-vapor and the variation of the air temperature in the adsorbent bed with time were measured under various inlet air temperatures and humidity and air flow rates. The completion time for the adsorption process was increased with decreasing air temperature and increasing the relative air humidity and the air flow rate. It was observed that the adsorption process of passing a moist air into the organic adsorbent bed was the isoenthalpy change. The data of Sherwood number for mass transfer in the present adsorption experiments were correlated by means of modified Reynolds number, Schmidt number and other non-dimensional parameters.