Acoustic fatigue in a piezoelectric ceramics has been measured by a new method based on the fracture mechanics concept. By using the method, a velocity of the acoustic fatigue crack growth has been measured as a function of stress intensity factor, separating from the crack initiation and final breakdown. The acoustic fatigue crack growth was observed in a narrow range of stress intensity factor K I between 0.4K IC and 0.45K IC, where K IC is fracture toughness, and the crack velocity was 3.7–8.2×10-13 mm/cycle.