Absract This research presents a nondestructive iection technique of bonding between a composite layer and an aluminum sheet by ultrasonic Lamb waves. Advantage of ultrasonic NDT is that, in practice a small change in adhesive conditions affects wave propagation and hence can be recognized by these waves. This study first develops lamb wave propagation equations in a 3-layer structure. One of these layers is an anisotropic composite and the other two are isotropic.Dispersion curve for this triple-layer material will be presented using global matrix method (GMM). A frequency of 2 MHz is applied and different phase velocities that cause various modes are characterized.In this purpose, the through-thickness stress flow distributions are investigated for each mode at frequency of 2 MHz. The first mode’s through-thickness stress fields, at 2 MHz, are more appreciable in the cohesive layer. This sensitivity is evaluated based on the energy that is transferred to the adhesive layer. The dispersion curves are also calculated using the FEM, modeling the plate as a tree-layer, 2D plane strain system.These signals can then be signal processed into dispersion curves, or in the frequency-wave number space (using the 2D-FFT and equally spaced, multiple transient output signals).The dispersion relations (when they are visible) from the FE results agree with those predicted by the GMM. For the experiment a specimen was made of the aluminum and composite plates that their thickness were 2 mm and 1.6 mm consecutively. The dimensions of the joint plates were 250*250 mm 2 . Thickness of adhesive layer (5-minute epoxy) was approximately 0.2 mm. For testing, a 1*1 in 2 disbond in the interface of aluminum plates were introduced by leaving the programmed area, free of cohesive (air gaps) when the plates were bonded. Experiments were made in a pitch-catch setup using two variable 2 MHz angle transducers, one as transmitter of the guided wave and the other as receiver. Although we used the four mode Lamb waves to iect disbond in the aluminum-cohesive-composite, good iection and detection exist for first mode whit 30° angle probe. This result derives from obvious reduction of amplitude of received signal for first mode. Key words NDT, ultrasonic iection , Lamb wave propagation equations, finite element analysis, aluminum sheet, adhesive material, anisotropic composite material.