The CNDO/2 calculations have been applied on cluster models for the representative T sites in faujasite to get atomic charge densities, wiberg bond orders and total energies. The chemical stabilities of suggested models for the dealumination mechanism were also explained in terms of total energies. The calculated charge densities and bond orders of cluster models have been changed remarkally according to the H⁺ attack. The calculated results showed the dealumination of faujasite in acidic solution was caused of Al-O bond weakening by acid attack.