Pulsed-laser deposited (Pb,Sr)TiO3 (PSrT) films on Pt/SiO 2/Si substrate at various ambient oxygen pressures (PO2) are investigated in this work. Films deposited at PO2 below 100mTorr exhibit the (100) preferred orientation and a tetragonal structure with larger tetragonality. In addition, films deposited at 80mTorr exhibit the most apparent ferroelectric properties in contrast to those deposited at 200mTorr. Moreover, films deposited at higher PO2 also exhibit longer lifetimes and higher breakdown fields due to their smaller leakage current density, in terms of the reduction of defects, compensation of oxygen vacancies (OVs), an improved interface and small cluster sizes. An energy band model reveals that fatigue properties of PSrT films are dominated by interfacial states at low P O2 and by deep trapping states at high PO2, which could be ascribed to OVs located at the interfaces and inside films, respectively.