The adsorption properties of ethylene on H-Faujasite (H-FAU) and H-ZSM-5 zeolites have been investigated by both the cluster and embedded cluster approaches at the MP2 and B3LYP levels of theory using the 6-31 G(d, p) basis set. The effects of the Madelung potential were found to be important. The calculated MP2 adsorption energy of -13.55 kcal/mol for the [C2H4]/H-ZSM-5 complex is larger than that of -8.2 kcal/mol for the [C2H4]/H-FAU complex. This is consistent with the experimental observation that the ZSM-5 is more acidic than that of FAU zeolite. The adsorption energy for the [C2H4]/H-FAU complex is comparable with the experimental estimate of about -9 kcal/mol for ethylene adsorbed on the H-FAU zeolite.