Abstract: The wear resistance of as cast hypereutectic Al Si alloy and of the alloys overheated at various temperatures has been investigated with an MM 200 friction and wear tester under dry sliding against AISI 1045 steel. The structure and the morphologies of the worn surfaces and wear debris have been examined by means of scanning electron microscopy (SEM). As the results, the wear resistance of hypereutectic Al Si alloy is increased considerably by overheating treatment. This is especially so when the alloy is subject to relatively high load friction and wear test. SEM observation of the structure and the morphologies of the worn surfaces and wear debris indicates that the primary silicon in the alloy matrix was broken during the friction, which leads to generation of micro cracks and holes near the deformed and non deformed regions of the alloy matrix. This gives rise to the wear rate of the as cast hypereutectic Al Si alloy. Therefore, the finer the primary silicon phase is, the more uniformly the alloy matrix distributes. Subsequently the higher the hardness of the matrix and wear resistance.