The main focus of this study is concentrated on the effect of mechanical milling on graphite-boron carbide hybrid reinforced ZA27 nanocomposites. With this respect, nano-sized graphite (Gr) and boron carbide (C) reinforced ZA27 matrix nanocomposites were fabricated via a combination of mechanical milling (MM) and hot pressing techniques. MM method was used to produce a ZA27-based hybrid nanocomposite (ZHNC) that nano-sized additives dispersed homogenously in ZA27 matrix. Microstructural and mechanical properties of the nanocomposites were scrutinized as a function of milling time using X-ray diffractometer, scanning electron microscope, hardness and tensile testing machines. Results show that MM method can be utilized for homogeneously distributing the nano-sized additives. Flake-shape morphology negatively influences physical and mechanical properties. It was also found that grain and particle size is decreased after 12 h milling process. With increasing MM time, homogeneous microstructure of the nanocomposite bulk materials was obtained and subsequently their mechanical properties were improved considerably.