Cluster model quantum chemical calculations have been performed to compare stabilization energies (E-st) of Zn2+ ions in four-, five-, and six-membered zeolitic rings. E-st was evaluated as energy of the reaction Zn2+/Z + H-2 double right arrow 2H(+)/Z + Zn-0. It was found that E-st substantially decreases in the series six-, five-, and four-membered ring, and this trend is essential to the understanding of the comparative adsorption ability and reactivity of Zn2+ in cationic sites of different zeolites. This conclusion was proved in calculations of the heterolytic dissociation of ethane, The molecular structure of active sites in ZnHY and ZnHZSM-5 zeolites and the question of the stability of small intrazeolite zinc oxide species are discussed.