In summary, the effect of oxygen vacancies on structural and electrical properties in epitaxial thin films of SrFeO3−δ (SFO) is studied, where SFO is a compound with multiple valance states at the B site. Various annealing treatments are used to produce different oxygen contents in the films, which results in significant structural changes in the fully strained SFO films. The out-of-plane lattice parameter and tetragonality increase with decreasing oxygen concentration, indicating the crystal structure is closely related to the oxygen content. Importantly, variation of the oxygen content in the films significantly affects the dielectric properties, leakage conduction mechanisms, and the resistive hysteresis of the materials. Leakage current mechanisms are found to shift from dominantly bulk-mediated trap-assisted tunneling to interface-mediated Schottky thermionic emission depending on oxygen vacancy concentration. Temperature dependence of vacuum annealed SFO thin film is investigated in the temperature range of 120 K–300 K, and results suggested a suppression of polarizability of the SFO thin film with decreasing temperature, as indicated by a reduction in the dielectric constant and tunability of the SFO film. These results establish the relationship between oxygen content and structural and functional properties for a range of multivalent transition metal oxides.