The micro and mesoporosity of natural and ion-exchanged (Cu(II), Zn(II) and Ag(I)) mordenites from Palmarito ore (Cuba) have been studied by adsorption of N2 at 77K, H2O at 300K and CO2 at 273K, and compared with other natural and synthetic mordenites with the main objective of explaining the previously reported excellent performance of the Cu(II)-exchanged mordenite in the selective catalytic reduction of NO. Palmarito ore possesses a high concentration of mordenite and a more open porosity than other naturally found mordenites, as determined from the adsorption of the probe molecules studied. The ion-exchange processes modify the micro and mesoporosity of the zeolite, resulting in more accessibility to N2 adsorption. In the case of the Cu(II) exchanged sample, the presence of CuO microcrystals on the surface causes an increase in the secondary porosity, with a subsequent enhancement of the capillary condensation at low relative pressures. These are some of the factors which explain the good catalytic performance of this sample.