Microstructure and mechanical properties of heat treated Al-Si alloy containing up to 10 wt% aluminum nitride (AlN) particles were investigate. In this work high purity AlN powder with different weight percentage of 0, 5, 7 and 10 were calculated as reinforced material to the metal matrix composites. The Al-Si matrix was prepared by a bottom pour stir casting technique. Heat treatment was performed by soaking and followed by an aged treatment. It was found that the AlN particles were scattered randomly distributed in the matrix composite. Ageing induced Si grain transformation into to spheroid shapes while Al dendrites tend to become finer. Ultimate tensile strength (UTS) had improved drastically from to 125MPa to 306MPa for un-aged Al-Si alloy and aged AlN 7 wt%. Fracture morphologies showed a pronounced feature with small dimples, tear ridges and micro neck particularly in the aged samples leading to a higher tensile value and increase in ductility. The presence of AlN particles in the alloys had improved the tensile strength by slowing down the plastic deformation during tensile test.