In the last years, the piezoelectric transducers of lead zirconate titanate (PZT) have been widely used in structural health monitoring (SHM) systems based on the electromechanical (E/M) impedance technique. Although many studies indicate the successful use of PZT in damage detection, some practical considerations still have to be considered in real applications. In this work, the effect of the transducer loading caused by mechanical impedance of the host structure is analyzed using an equivalent electromechanical circuit. Tests were performed on structures with various sizes and the results show that the transducer loading significantly reduces the sensitivity of the system for detecting structural damages.