This study describes the effect of cation exchange (Ni 2+ and Ca 2+ ) on the adsorption capacity and breakthrough time of a natural zeolite (clinoptilolite) employed in the ethanol dewatering process. The results obtained showed that modification of clinoptilolite (Clin) by cation exchange led to a decrease in the breakthrough time and water adsorption capacity in the order: Ca-Clin > Ni-Clin > Clin. In addition, characterization of the prepared clinoptilolite samples by BET, XRD and SEM techniques showed that no degradation of crystallinity had occurred, although the pore volumes of both cation-exchanged samples had increased as well as the surface area of the Ni-Clin sample.