The ion exchange properties of Na-ß-alumina were studied. Samples of Na-ß-alumina treated in a CaCl2 melt at 1173 K and then examined with X-ray energy dispersive spectroscopy. We were able to exchange the sodium ions completely for bivalent calcium ions. The calcium aluminate compound (CaO·10Al2O3) was characterized by powder X-ray diffraction and ²7Al NMR measurements and with these methods it was proved to have the ß-alumina-type structure. Heat treatments at 1173 K and 1373 K showed that the compound decomposes to CaO·6Al2O3 and Al2O3 and, therefore, is metastable at these temperatures.