The electric conductivity of ZnF2-ALF(3)-PbF2-LiF glasses has been studied in the frequency range 10 Hz-2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F- ions by Li+ ions. Small values of the stretching exponent beta are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.