The BST films prepared by RF magnetron sputtering were processed in an O2-plasma treatment system.Experiment results indicate that the leakage currents and dielectric loss of the films were effectively reduced.The possible mechanism may be attributed to the passivation of oxygen vacancies,which act as electric conduction paths of leakage currents.The effect of the time of oxygen plasma treatment on the dielectric properties of BST thin films was also investigated and optimized.When the films were treated for 5min,the loss tangent decreased to 0.7% and leakage current density decreased by two orders of magnitude (7.96× 10-9 A/cm2),compared to that of the films without treatment.However,it was found that exposure in oxygen plasma for too long time would damage the surface of the film.