In this study, the dehydration of natural gas by a bed of 5A zeolite pellet was theoretically studied. In developing the mathematical model, heat and mass balance equations in gas phase were employed while both convective and diffusive terms as well as adsorption of all adsorbable components were considered. In calculating the global mass transfer rate, external gas resistance to mass transfer was neglected. The 5A zeolite pellets have a bidisperse pore structure and mass transfer within the macropore as well as the micropore structures were considered. Macropore mass transfer rate was calculated via the Fick’s law and the LDF model was tested for expressing the rate in the micropores. The energy balance equations for the two, gas and solid phase were discretely employed. The packed bed wall was assumed to be adiabatic and of negligible heat capacity. Pressure drop in bed was represented by the Ergun equation. An extensive collection of literature gas-solid equilibrium data was utilized and correlated by the Langmuir, Langmuir-Freundlich, Toth and dual-site-Langmuir models and the dual-site-Langmuir proved most suitable for predicting multicomponent adsorption equilibrium. In this study the effects of temperature and pressure on adsorption rate were investigated. Application of conservation laws resulted in a set of nonlinear differential and algebraic equations that were numerically solved. The method of finite volume and implicit discretization was employed in solving the partial differential equations involved. The simulation procedure was validated by comparing the results with published data. The results of this study indicated that the assumptions of local thermal equilibrium between the gas and the adsorbing pellets as well as lump heat transfer parameters in the pellet are acceptable. Also the LDF mass transfer model in the adsorption bed was tested and the results revealed the model was unable in predicting adsorption rates.