The physical and electrical properties of La2O3 with and without an Al2O3 capping layer deposited by remote plasma atomic layer deposition were investigated. The electrical properties of the La2O3 films degraded due to the formation of lanthanum hydroxide after being exposed to air. The results of x-ray photoemission spectroscopy showed that the quantity of OH groups absorbed increased after exposure to air. For La2O3 with an Al2O3 capping layer, however, the electrical properties of the film did not change substantially because the capping layer effectively suppressed the formation of lanthanum hydroxide. The capacitance of the La2O3 decreased more than 30% after exposure to air, while La2O3 with an Al2O3 capping layer decreased by only about 4%. The VFB value of the La2O3 with an Al2O3 capping layer was near zero, and the hysteresis was about 120 mV. The leakage current densities of the film were maintained below 5 × 10−7 A/cm2 up to −15 MV/cm and the effective breakdown field was about −23.5 MV/cm.