In this study, an attempt has been made to determine the effect of an AlN reinforcement size on properties of aluminum alloy matrix composites produced via mechanical alloying/uniaxial hot pressing. Composite samples were prepared using pre-alloyed AA7475 powder with 10wt.% of AlN additions of differing average particle sizes: <40μm, ∼1μm or <1μm. Powders were milled in a high energy ball mill for up to 40h and then hot pressed in vacuum at 380°C/600MPa. Milled powder analysis revealed that addition of micro-sized hard reinforcing phase allows to achieve a higher level of crystallite size refinement as compared with submicron reinforcement, under the same milling conditions. The SEM/TEM microstructures of compacted samples confirmed uniform dispersion of the ceramic phases independent of the size. All of the composites were characterized by fine matrix grain size (<200nm) and a high density of even finer intermetallic, Zn, Cu, Mg or Fe rich precipitates. The obtained hardness results were highest for ∼1μm AlN addition – near 320 HV which is an 30% improvement over the matrix itself. The best properties of composites reinforced with intermediate particles suggest that the achievement of a compromise between the structure refinement during MA and grain growth restraint during hot pressing is of a particular importance in composite materials produced in this way.