In this work, the effect of design and operating parameters on the performance of a multilayer desiccant packed bed was theoretically and experimentally studied. In the experimental work, a silica gel packed bed of eight layers has been studied. The transient value of the mass of adsorbed water and desorbed water was measured for different values of the bed length. The theoretical model shows the dependence of the dimensionless value of water content in the bed on the dimensionless time. Also the model shows that the dimensionless temperature depends on the bed characteristics and bed water content. The effect of inlet air humidity and velocity on the adsorption process for each bed layer was studied at different inlet velocities and at different air humidities. The effect of inlet temperature on desorption process for each packed bed layer was also studied at different inlet temperatures. The theoretical model also introduces an equation which can be used to predict the optimum bed length. Also, the optimum length of the bed can be recommended from the experimental results according to the operation time. Good agreement between experimental and theoretical results was found. (C) 2008 Elsevier Ltd. All rights reserved.