The aim of this study is to investigate the failure of cracked aluminum plates repaired by one-side composite patches under fatigue loading using Acoustic Emission (AE) and fractography images. Rectangular specimens made of 6061 aluminum alloy with central through thickness pre-cracks were repaired using glass/epoxy laminated patches. The specimens were subjected to the fatigue loading and AE technique was employed to monitor the effect of the repair patch on the damage progression. First, different stages of damage evolution were studied based on the mechanical data and fractography images. Then, the AE energy utilized to characterize failure process of the specimens. To this aim, AE signals of the aluminum cracking and adhesive layer failure were discriminated according to their energy content. The effect of patch thickness and layup on the failure behavior of the specimens were also studied. Finally, it is concluded that AE is a powerful technique to characterize the failure process of a repaired cracked aeronautic structure by composite patches.