Transient adsorption/desorption characteristics of spherical particles of silica gel (about 3 mm in diameter) in a fluidized bed have been studied experimentally. To control the humidity of inlet air, a humidifier is designed and fitted in a proper location in the system. The system is well instrumented to measure the inlet and outlet air parameters as well as bed temperatures during the experiments. A simplified analytical model with isothermal adsorption assumption is developed. Transient values of the mass of adsorbed water in the bed, rate of adsorption and water content in silica gel particles are evaluated from the experimental measurements. Experimental values of the volumetric mass transfer coefficient and the dimensionless value of water content in the bed are plotted and compared with values obtained from the analytical model for different operating conditions. Good agreement is found at the first period of adsorption, when the adsorption is nearly isothermal. Successive increase in bed temperature, results in increase in the discrepancy between the results of the analytical model and experimental data. Accordingly, the isothermal model could be applied with reasonable degree of reality for systems with shorter adsorption/desorption cycles. The drop in air humidity is highly affected by its inlet value. It is found that the maximum decrease in air humidity occurs at the beginning of adsorption and the rate of water vapor adsorption increases with the increase in the inlet humidity. (C) 2010 Elsevier Ltd. All rights reserved.