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The carbonatation of La2O3oxide and the decarbonatation of lanthanum carbonate phase La2O2CO3are investigated using thermal and thermogravimetry analyses under CO2gas flow. The initial phase La2O3is first elaborated from pyrolysis of a LaOHCO3precursor. Then, thermal and thermogravimetry analyses are carried out under CO2flow, as temperature increases then decreases. The carbonatation kinetics of La2O3is determined at three fixed temperatures. Electrical impedance spectroscopy is performed to determine the electrical responses associated with ionic mobilities and phase changes, in the temperature range 25 to900∘C. The electrical conduction during heating underCO2gas flow should be linked to two regimes of ionic conduction of the carbonate ions. From these electrical measurements, the ionic mobility of carbonate ionsCO3  2−is found to be close to 0.003 ⋅10−4 cm2 s−1 V−1at750∘C for the monoclinic La2O2CO3phase.