The effect of repeated in-service inspection on the reliability degradation due to fatigue crack growth is investigated based upon a stochastic fracture mechanics. A method to evaluate the failure probability under repeated inspections is first discussed on the assumption that the components is exchanged when cracks are detected. The results are then applied to investigate how the reliability of structures behaves under repeated ultrasonic inspections. It is clarified that the inspection policy and the stochastic nature of the fatigue crack propagation process have significant effects on the reliability degradation of the structural components.