Moisture absorption is a big problem of lanthanum oxide (La 2O3) as a high permittivity (k) gate dielectric which can degrade properties of La2O3 films. In this study, two possible mechanisms have been proposed. One is oxygen vacancies in La 2O3. The other is the intrinsic reaction between La 2O3 and H2O due to the small lattice energy of La2O3. To suppress these two reactions of H2O with La2O3, two solutions have been proposed respectively. One is the ultraviolet (UV) ozone post treatment to suppress the moisture absorption through healing the oxygen vacancies in La2O3 films. Our experiment results show that UV ozone treatment can suppress the moisture absorption of La2O3 film. The other solution is to dope a larger lattice energy oxide into La2O3 to suppress the intrinsic moisture absorption reaction. We have demonstrated experimentally that the Y2O3 doping (LaYOx) films show much stronger moisture resistance than La2O3 film.