Grand canonical Monte Carlo simulations were used to study the effect of dealumination on adsorption of xenon in an idealized structural model of Na-mordenite. Simulations were carried out at SiAl ratios of 5, 11, and ∞, chosen to represent prototype cation occupancies. A recent experimental study of xenon adsorption in mordenites with different SiAl ratios found unexpected nonmonotonic trends. In disagreement with experiment, the isotherms of our idealized zeolite changed monotonically with the degree of dealumination. This trend supports recent observations that significant structural changes result from dealumination.