Abstract: In order to detect defects in pipes effectively, by using PZT transducers, which are attached axis-symmetrically around the pipe, to generate and receive ultrasonic guided waves, the relationship between the echo peak-to-peak amplitude of echoes of the pipe end and defect and the exciting frequency was studied. The influence of the transducer's number to the signal was researched and the best range of frequency which was used to generate ultrasonic guided waves was determined. Experiments demonstrate that, the amplitude response is effected by the intrinsic characteristic of transducers. The experimental results show that many choices of transducer number and exciting frequency can be made to produce a good result and be kept for the reference of the pipe defect inspection with guided waves.