Bi5Nb3O15 (B5N3) films grown under a low oxygen partial pressure (OP) of 1.7 mtorr showed a high leakage current density of 0.1 A/cm2 at 1.0 MV/cm. However, the leakage current density decreased with increasing OP to a minimum of 5.8 times 10-9 A/cm2 for the film grown under 5.1 mtorr due to the decreased number of oxygen vacancies. This film also showed an improved breakdown field of 2.2 MV/cm and a large capacitance density of 24.9 fF /mum2. The electrical properties of the film, however, deteriorated with a further increase in OP, which is probably due to the formation of oxygen interstitial ions. Therefore, superior electrical properties for the B5N3 film can be obtained by careful control of OP.