Aluminum matrix composites reinforced by ceramic particles are one of the promising materials for engineering applications. Joining of aluminum matrix composite components can be done by various methods based on fusion welding and solid state welding. Friction welding, (FW) as a solid state welding process, has some advantages over fusion welding such as smaller heat input, lower residual torsion and thermal stresses and lack of undesirable microstructure from solidification. In this research, aluminum matrix composite powders containing 5, 10 and 15 wt% of Al 2 O 3 nano particles were produced by mechanical milling. Then, bulk specimens (42×12×12 mm) were produced by hot pressing of mechanically milled powder. Finally, the bulk samples were welded to 2014 Al alloy with constant welding parameters. The results showed that after 5 hours of ball milling, an Al-Al 2 O 3 nanocomposite structure with an Al grain size of 75 nm was achieved. This structure remained unchanged after hot pressing. The increasing Al 2 O 3 content increased the hardness value of bulk samples but reduced their density and bending strength. It was revealed that the fracture of bulk nanocomposites occurred by interparticle brittle fracture mechanism. Microstructural observations of dissimilar welds of Al-Al 2 O 3 nanocomposites and 2014 Al alloy showed a fully plasticized region (Z pl ) in joint boundary and a partly deformed region (Z pd ) in the region far from joint line in both side of the weld. Plastic deformation, mechanical mixing and high temperature near weld line led to a uniform structure Z pl region for nanocomposite side with no traces of interparticle boundaries and lamellar structure, resulting from milling process. Increasing the amount of Al 2 O 3 particles in nanocomposite, increased the heat produced during welding processes. The amount of axial up-set (shortening) and the width of Z pl region in case of sample with 5wt% Al 2 O 3 was maximum, owing to high plastic deformation. In all cases, hardness of weld zone in nanocomposite and 2014 Al alloy side were reduced in comparison with base metal, but it should be note that hardness value of joint boundary in 2014 Al alloy side was not the minimum value. While the bending strength of nanocomposite significantly reduced by increasing the reinforcement content, fracture in all cases were found to occur by brittle mechanism with cleavage morphology and that the crack was developed in the nanocomposite side. The results of friction welding of nanocomposite containing 5wt% Al 2 O 3 , demonstrated that the axial up-set and the width of Z pl region were increased by increasing the frictional forging pressure and also increasing the rotation speed. Also TEM study of Z pl region in these system, showed the uniform distribution of Al 2 O 3 nano particles, but Al nanocrystalline structure did not remain in nano sized scale in these zone probably because of formation of recrystallized grains. Keywords: , Nanocomposite, Friction Welding, Al 2 O 3 Nano Particles, 2014 Al Alloy, Mechanical Milling, Hot Pressing, Dissimilar Welding.