Abstract: Upon being subjected to the external load , acoustic emission (AE) may occur f rom mat rix cracking , interface debonding , fiber f racture , etc in composite materials. U HMWPE/ HDPE composite materials were experimented to determine the event amplitude content of AE signals under tensile loads. Special specimens , designed tofail under well-defined modes such as mat rix plastic deformation and cracking , fiber-mat rix debonding , fiber breakage , delamination , etc were tested under the loads f rom zero to failure. The f racture surfaces of the specimens wereobserved by a scanning elect ron microscope ( SEM) . The AE signals were distinguished as being released fromseveral special types of damage. AE measurement s were performed subsequently for different types of U HMWPE/HDPE quasi-isot ropic laminates under the same loading conditions. The correlations are established between thedamage modes and acoustic emission event s amplitude of special specimens which exhibit the dominant damage mechanisms. The AE characteristics of damage growth processes and the fracture mechanisms in U HMWPE/ HDPEquasi2isot ropic laminates are revealed. Accumulative numbers of acoustic emission event s for different types ofU HMWPE/ HDPE quasi-isot ropic laminates vs tensile st ress curves are different from each other ; the correspondingloading levels of their same type of damage occurrence are not equal. The results show that ply stacking angles andsequences affect remarkably the damage growth process of these laminates. It is verified that the final fracture ofthese materials is caused by severe interlaminar delamination.