Oxygen transport under different cathodic overpotentials was investigated at the LaMnO3 film/Y2O3 stabilized ZrO2 interface. A stable isotope oxygen (O-18) was adopted as a diffusion marker at 1073 K under cathodic polarization, and the quenched samples were analyzed by secondary ion mass spectrometry. The O-18 diffusion profiles indicate the higher diffusivity of O-18 in LaMnO3 film with the higher cathodic overpotentials. The introduction of oxygen vacancies by the cathodic polarization can change the diffusion profiles of O-18 in the LaMnO3 film. The diffusion profiles of oxygen in LaMnO3 film under the cathodic polarization were calculated from the literature data of oxygen content in LaMnO3 as a first estimation. The calculated diffusion profiles showed a similar trend with the measured ones, but different concentration in the LaMnO3 film under the higher polarization.