Dealuminated mordenites depicting SiO2/Al2O3 molar ratios in the range 10-206 were analyzed through adsorption methods. The Type I-IV hybrid shape of the N-2 adsorption isotherms at 76 K on dealuminated mordenites indicated rather high micropore contents, though some amount of mesopores of slit-like geometry was also present. Micropore volumes and sizes were measured through alpha(S) , t , and DA-plots, as well as by the NLDFT approach. Results indicated that mordenite dealumination caused micropore opening and widening as well as the emergence of further slit-like mesopores; even though a slight structural collapse toward creation of mesopore zones occurred at high dealumination extents.