The objective of this research is to locate and evaluate wall thinning in pipe elbow by a non-contact guided wave technique with laser source as a transmitter and air-bone transducer as a receiver, respectively. Wall thinning of carbon steel pipe is one of the most serious problems in nuclear industry; especially the one in carbon steel pipe elbow caused by FAC (Flow-Accelerated Corrosion). Therefore, development of a robust NDE technique for the pipe elbows is essential for safe operation of nuclear power plants. Specimens used in this study were carbon steel which is widely used in real nuclear power plants. The geometry of wall thinning was given as 120mm extent, 80mm-length and 5mm-depth. The L(0,1) and L(0,2) dominant modes group shows a promising variation in the ultrasound guided wave data analysis based on the response obtained by the laser generation/air-coupled detection system. The trends of these characteristics and subsequent signal processing were used to estimate the size and location of wall thinning.