Thermal conductivity, K, of free-standing air plasma sprayed (APS) thermal barrier coatings (TBCs) after exposure at temperatures of 1100, 1200, and 1350 °C for 3, 10, 17, 24, and 120 h was measured using laser flash (LF) technique and differential scanning calorimeter (DSC), and correlated with the spectra of electrochemical impedance spectroscopy (EIS). High-temperature exposure of TBCs increases the thermal conductivity as well as the electrochemical conductance, C t T , with an increase in exposure temperature and exposure time. A linear relationship between thermal conductivity, K, and electrochemical conductance, C t T , has been found. The result has demonstrated that electrochemical impedance technique holds the promise enabling to assess and monitor the thermal conductivity of free-standing TBCs.