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This paper herein studies subcritical crack growth ( SCG) behavior of a perovskite-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ ( BSCF) as an oxygen transport membrane material. The SCG behavior of BSCF is evaluated by a constant load method and constant stress rate method at room temperature ( RT) and 800°C in air, respectively. The low crack velocity measurements are carried out by ring-on-ring bending tests while the high crack velocity measurements by compact tension tests. The stress rates vary approximately from 0.1012 to 101.2 MPa/min. The fracture stress increases with increasing stress rate at 800°C. The SCG parameter, n, of BSCF is determined to be 24.32 and 13.83 at RT and 800°C in air, respectively. This indicates that BSCF is more susceptible to SCG at 800°C. The strength-probability-time ( SPT) diagram is constructed for design proposes. The stress for a lifetime of 40 years should not exceed 27.21 MPa at RT or 4.53 MPa at 800°C to assure a failure probability below 1%. [ABSTRACT FROM AUTHOR]