Al-Si-Mg reinforced with Al2O3 nano particles have been made by stir casting method. The vortex produced by stirrer is to distribute the Al2O3 nano particles in the molten aluminium. The volume fraction of Al2O3 nano particles was varied from 0.5, 1, 2, 3, to 5 Vf%, while the addition of magnesium was 3 Vf% as wetting agent to improve the wettability between Al2O3 nano particle and Al-Si-Mg matrix. The effect of Al2O3 on characteristic of Al-Si-Mg composites was studied. It is found that the presence of Al2O3 nano particle led to significant improve in mechanical properties, especially at addition of 0.5 Vf% Al2O3. The ultimate tensile strength reached to 154 MPa with 10.24% elongation, while the hardness reached to 37.7 HRB followed by decrement in wear rate. The porosity level tend to increase with increasing of Al2O3 and caused decrement in mechanical properties.