Abstract: The total electric conductivity of Na₃AlF₆-Al₂O₃ slag and the effect of added CaO on the electric conductivity of the slag were investigated by the Ac impedance method of electrochemistry. Equivalent circuits were proposed according to the measured impedance spectra. EvolCRT electrochemical software was used to simulate the impedance data. The correlations of conductivity to slag composition and temperature were studied. The addition of CaO increases the electric conductivity of the system.