In this study, AlCuMg-B4C nanocomposites reinforced with the B4C particles were produced using the mechanical milling and hot pressing method. The AlCuMg-B4C nanocomposite powders were milled for up to 25h and then hot pressed in vacuum at 560°C and 300MPa. The microstructure, density, hardness and tensile strength of the AlCuMg-B4C nanocomposites were investigated as a function of the milling time and the B4C content (wt%). The results show that the hot pressed density of the AlCuMg-B4C nanocomposites decreased with increasing B4C content and increasing milling time. The unreinforced AlCuMg alloy showed a high relative density of 99.2%, which is much higher density than that of the AlCuMg-15wt% B4C nanocomposites produced with a milling time of 25h. The hardness of the hot pressed nanocomposites was significantly higher than that of the hot pressed nanocomposites produced by using the conventional powder metallurgy. AlCuMg-10wt% of B4C nanocomposites produced with milling time of 6h exhibited the highest tensile strength of 332MPa.