The CNDO/2 method was used to investigate the electronic structure and the interaction of CO mole-cules with the exchanged cations in the zeolites which have various Si/Al ratios. The electron densities of zeolites increased and the bond orders of T-O generally decreased with decreasing the Si/Al ratio. The strength of bond between CO molecules and the exchanged cations in the zeolites increased in the following order:H⁺<Na⁺<Ca²⁺<Li⁺<Mg²⁺< Be²⁺. The interaction strength increased obviously with the electro-static field of cations. The C-O bond orders of CO molecules interacting with the exchanged cations in the zeolites in-creased compared to those of free CO molecule. This was in a good agreement with IR results.