Na2CO3-K2CO3 (56-44 wt.%) eutectic composition was vacuum-impregnated into porous Al2O3 (alumina) and to ZrO2: 3 wt.% MgO (magnesium-partially stabilized zirconia, Mg-PSZ) at the molten eutectic temperature. Porosity was achieved in the two compounds by addition and thermal removal of the eutectic composition before impregnation. The parallel surfaces of disk-shaped impregnated compositions were observed in a scanning electron microscope. The CO3 2- carbonate ion conductivity of the two composite ceramics was measured by electrochemical impedance spectroscopy in the 5 Hz-13 MHz frequency range from 470??C to 780??C. The permeation of the carbonate ions via eutectic composition through the ceramic membranes was ascertained by the threshold temperatures of the onset of the carbonate ion percolation: 660??C and 720??C for alumina and Mg-PSZ, respectively.