The changes of microstructure of cooked chicken breast treated by ultra-high pressure treatment(UHP) were observed, for the further study of UHP on cooked chicken breast. Results indicated that the gap between the muscle fibers decreased, endomysial disappeared gradually, and the structure of muscle fibers was more closely. Meanwhile, muscle fiber diameter and rate of juice leakage increase could be resulted from UHP significantly. Myofibril was fragmented and gelated obviously when the pressure was over 400 MPa. The microstructure of cooked chicken breast treated by UHP could explain the changes of jucie leakage, texture and edible quality.