In this study, we aimed to investigate the effects of some specific zeolitic parameters on the retention properties of metal-exchanged faujasites (X and Y) for methyl iodide. In the first part, the nature of exchangeable cation (H + , Na + , Cu + /Cu 2+ , Ag + , Pb 2+) is discussed. In order to link the materials properties with the adsorption behaviour, the state and location of the exchanged transition metals after calcination at 500°C were first investigated using N 2 sorptiometry at 77K, DRS-UV-Vis spectroscopy, XRD and FTIR of adsorbed CO and NO. Adsorption capacities at breakthrough and saturation were obtained from CH 3 I breakthrough curves obtained at 100°C, this temperature being relevant to severe nuclear accident conditions. From the I/M ratio computed at saturation of the adsorbents by CH 3 I vapors, it was found that the efficiency of iodine trapping follows the order Cu + /Cu 2+ > Ag + >> Pb 2+ > Na + > H +. This efficiency roughly followed the trend of the different cations to form stable MI x precipitates from CH 3 I. Nevertheless, for nuclear application, it was found that Ag/FAU are preferred over Cu/FAU, due to the propension of the latter to oxidize CH 3 I to I 2 , which slips out of the sorbent bed at 100°C. The effect of the preparation method (ion-exchange vs impregnation) is then discussed for Ag/Y zeolites having different Si/Al ratio (2.5 and 40) but similar silver content (23 wt%). It is found that the silver oxidation state and silver dispersion have important effects on CH 3 I adsorption/desorption.