In this article, the complete characterization of the interface delamination in a composite T-joint using ultrasonic guided Lamb waves is discussed. Correlation between the numerically simulated and experimentally obtained B-scans was established. In the B-scan images, different Zones were identified and could be utilized for differentiating the healthy and delaminated T-joints. The length and the width of delamination were computed from traversing the transducers in two orthogonal directions (i.e. called the B-scans, and the D-scans). For the first time, backward propagating mode (called Turning Lamb Modes) that are generated at corner of the T-joint was observed and verfied. Using a single linear line scan of the Turning Lamb Modes, both the width and length of interface delamination could be computed. In the present study, the experiments were carried out employing air-coupled ultrasonic transducers. © 2011 Elsevier Ltd. All rights reserved.