The pipeline is playing an important role in industry nowadays. However, the inner wall of pipeline may suffer corrosion after a long service time. When excessive corrosion occurred, not only the transported material inside the pipe will let out but also serious accident may be induced. So, it¡¦s necessary to monitor pipeline thickness regularly. Conventionally, since most piping systems were subjected to high-temperature working environments, hence if an operator intend to examine the thickness of a pipeline, the whole piping system need to be shutdown and resulted in financial losses. Therefore, to develop on-line thickness measurement technique for pipelines subjected to high-temperature working environment is indispensable. ¡@¡@In this study, low-cost PZT sensors (Pb(ZrxTi1-x)O3), which can sustain high-temperature working environment, were used to execute the thickness measurements. A single PZT, which was bonded on the surface of a pipe as an actuator and a receiver simultaneously. Then, by utilizing the GUI(Graphic User Interface) system, which was designed in this study, the echo signal can be analyzed and the thickness of the pipe can be determined on-line and automatically. It is noted that the wave speed changed as environmental temperature increased. So, in this study, by using A36 steel plates and steel tubes as a specimens, a modified temperature versus wave velocity curve was proposed.. The experimental results showed that non-conservative thickness measurements will be obtained if modified wave speed was not adopted when working temperature increased. keywords¡GThickness measurement, PZT sensor, GUI system, Modified wave velocity curve.