Ionic conductivity curves of powder zeolite Y and mordenite encapsulating initially cobalt, nickel or copper cations, was determined by the shift of the cut-off frequency of the imaginary part of their complex impedances for temperatures lower than 650 ◦C. We have shown that zeolite Y containing nickel cations has 1 eV as activation energy in the range of temperature [530–600 ◦C], and with the addition of a small quantity of lithium its conductivity curve has undergone a shift towards lower energies. In addition, in the range [445–600 ◦C], cobalt cations in zeolite Y have a conductivity coefficient in the vicinity of [0.89–2.77]×10−6  −1 m−1 and activation energy 0.88 eV. With the lithium addition these values was changed, respectively, to [0.13–1.44]×10−6  −1 m−1 and 1 eV in the range [405–600 ◦C]. The same observations were obtained for copper cations in mordenite. The conductivity of this sample was changed from [1.12–4.25]×10−6  −1 m−1 in the narrowrange [550–650 ◦C] to [0.06–4.04]×10−6  −1 m−1 in the wider one [370–650 ◦C] after lithium addition. © 2007 Elsevier B.V. All rights reserved.