Todays, nano-structure aluminum matrix composites are widely used in many industrial applications due to their superior properties such as high strength to weight ratio. However, joining problems of these composite materials is a challenge which limits their applications. Mechanism of a nanostructured sheet of metal-matrix composite of Al/Al 2 O 3 reinforced by micro metric alumina particles was investigated. Transient liquid phase (TLP) diffusion bonding method was used as the joining and the effects bonding temperature and time on the joint properties were investigated. Nanostructured sheet samples of Al/5wt.% Al 2 O 3 were produced by accumulative roll bonding (ARB) and a thin interlayer of pure copper was deposited on one side joining surface by electro-deposition technique. Optical microscopy and scanning electron microscopy (SEM) were used to investigate the structure of sheet components, bonded interfaces and joint fracture surfaces at different conditions. X-ray diffraction patterns were utilizied to investigate the aluminum crystallite size in the nanostructured sheet components. The average size of grain was about 92 nm. Then were no significant changes in the crystallite size during TLP bonding. Consternation of alumina particles, micro-cracks and porosity were found in the joint areas that were filled from ?-Al solid phase and fine CuAl 2 precipitated particles. The filled areas increased as the joint temperature increase. It is due to a higher amount of the molten material produced during joining. Moreover, the amount of CuAl 2 precipitated particles reduced as the joining temperature increased, resulting in reduction of the hardness of the ?-Al solid phase in the joint area. The shear strength of the bonded joints was also evaluated using a tension test system. The maximum shear strength (82% of the base metal shear strength) was achieved at the bonding temperature of 590°C and process duration of 30 minutes. Analysis of the fractured surfaces showed plastic deformation, shear dimples and partially ductile failure. Some alumina particles were observed on the fractured surface. At low joining temperatures, the joint strength improved by incresing bonding time, whiles at high joining temperatures, the joint strength decreased due to reduction of CuAl 2 particles in the ?-Al solid phase. Keywords : Nanostructur