A mathematical model is developed for hydrogen encapsulation in Cs ion-exchanged zeolite A. In comparison with the previous mode[2] on encapsulation, the present model correctly considers the route to -cage encapsulation in that hydrogen molecules are allowed to enter into a -cage only from the neighboring -cage through toe O₆-window connecting the two cages. When the model is applied to temperature programmed decapsulation, excellent agreements were observed between the model predictions and the experimental data. In the investigated range, no influence of the encapsulation pressure was found on the diffusivity through -cages and on the mass transfer coefficient between the two types of cages. Also the encapsulation temperature had no effect on the isotherms of -cage concentration versus -cage concentration, indicating that the energy level of the hydrogen molecule is the same in both cages.