This paper proposes a piezoelectric sensor/actuator self-diagnostic procedure based on the principle of piezoelectric impedance technology to ensure the effective operation of the structural health monitoring (SHM) system. The premise of this procedure is to track the changes in the capacitive value of piezo electric materials resulting from the degradation of the mechanical/electrical properties and its attachment to a host structure, which is manifested in the im aginary part of the measured electrical admittances. Experiment is carried out on a cantilever beam attached with a PZT sheet to demonstrate the feasibility of the proposed procedure. The results are in good agreement with theoretical anal ysis that, compared to the case of good PZT transducers, the debonding between PZT transducers and the host causes an upward shift in the slope of the imaginary part of the admittance while the crack PZT transducers causes a downward shif t in the slope. The degree of the damage is proportional to the change of the capacitive value.