Synthetic zeolites have shown great potential for a number of applications in various fields such as adsorption, separation and ion exchange. They have unique structural properties such as uniform pores, high surface area, high ion exchange capacity and high thermal stability [1]. Synthetic NaX zeolite is composed of eight sodalite cages joined through six-membered oxygen rings in a tetrahedral arrangement. It has also supercage accessible through twelve-membered oxygen rings as seen in Fig. 1 [2]. The negative charges of the AlO 4 units which built the framework are balanced by exchangeable cations. These cations depending heavily on the size, charge density and distribution of cations in the porous structure play a very important role in adsorption, dehydration and ion exchange properties. The water and other adsorbate molecules are loosely bound to these cations. The cations can be introduced into the supercages to affect acid-base properties of zeolite. CO 2 is a small, non-polar, weak acidic molecule and can be adsorbed on the surfaces having basic character. The basic properties can be increased with the aluminum content of the zeolite structure with decreasing cation electronegativity. Besides to the properties mentioned above, the quantitative structural properties of NaX zeolite based on thermal analysis (thermogravimetric analysis (TG), differential scanning calorimetry (DSC)) data are employed to gain quantitative information about the coordinated water in channels and cages of the zeolite [3]. Based on dehydration of zeolites, water is classified as loosely bound water, zeolitic water and crystal water [4]. The cations located in the cavities and the channel walls are coordinated with water molecules which give rise to dehydration behavior of zeolites. Dehydration behavior of NaX zeolite depends on the amount and type of exchangeable cation, the Al/Si ratio, the presence or absence of H 2 O, time and temperature [5]. Dehydration enthalpy change and thermal stability can be determined by using thermoanalytical techniques [6].The objective of this work is to determine the effect of cation (Li + , K + , Ca 2+ and Ce 3+ ) on the CO 2 adsorption and the dehydration behavior of the NaX zeolite. Analysis and Calorimetry, Vol. 94 (2008) It was observed that both dehydration and CO 2 adsorption properties are related to cation introduced into zeolite structure.