Ion-exchange of Na56Y with Cs+ cations has been monitored by Cs-133 MAS NMR. The observed signals are assigned to the extraframework cation sites based on the incremental ion-exchange process, as well as the adsorption of the tungsten hexacarbonyl molecule, W(CO)(6). The latter process selectively shifts the signals of alpha-cage Cs+ ions in the zeolite host. Subsequent oxidation of adsorbed W(CO)(6) to form encapsulated tungsten(VI) oxide also has a strong effect on the position and line width of the signals from the alpha-cage Cs-133(+) ions. Because of the relatively low quadrupolar coupling of Cs-133 nuclei in Na-(56-x)CsxY, their MAS signals do not suffer from extensive second-order broadening, as is the case of Na-23 nuclei. Therefore, Cs-133 MAS can be usefully applied to study zeolite ion-exchange and adsorption processes.