Aluminum-based metal matrix composites (MMCs) are ideal materials for structural applications in the aircraft and automotive industries on account of their excellent mechanical characteristics and low cost component production with respect to other alloys. Aluminum metal matrix composites are light-weight and have high strength and noticeable specific elastic modulus. In present study, nanocomposites of Al6061 alloy reinforced by Al2O3 were produced and optimized using ball milling and hot pressing method. To produce nanostructured Al6061, milling up to 30 hours was performed on initial Al6061 chips with an average particle and grain size of about 500?m and 130?m, respectively. A planetary ball mill with the rotational speed of 500 rpm, ball to powder weight ratio of 10:1, high purity argon protective atmosphere, and 0.1wt% stearic acid was employed. Morphological and structural changes of Al6061 were examined during mechanical milling using Scanning Electron Microscopy (SEM) observations and X-ray Diffraction (XRD) analysis. Moreover, thermal stability and structural changes of nanostructured Al6061 were evaluated via isothermal heat treatment at various temperatures for different times. (0-5)vol% Al2O3 nanoparticles which were dispersed ultrasonically were then added to the 15h milled Al6061 powders. To achieve a good physical contact between the reinforcements and matrix, these mixtures were again milled up to 15 hours. Mechanical milling of nanocomposite powders for 15h, hot pressing at 400°C and 128MPa for 0.5h was selected as optimized parameters for bulk nanocomposite and nanostructured preparation. In order to probe the effect of hot pressing on structural changes, XRD analysis was done on nanocomposite samples before and after consolidation. Variation of relative density of consolidated samples versus Al2O3 nanoparticles volume percent was measured using Archimedes technique. Hardness and compression tests were applied on bulk samples in order to evaluate their mechanical properties. Wear behavior of nanocomposites were characterized using pin-on-disk test method, as well. Moreover, nanocomposites with 3vol% Al2O3 in the micron sizes were produced and their wear behavior was investigated; as a result, a comparison between tribological behavior of Al6061-3vol%Al2O3 nanocomposites with nano and micro size reinforcement particles was done. . Keywords: Al6061-Al2O3 nanocomposites, Mechanical milling, Hot pressing, Mechanical properties, Wear behavior