Abstract: At present there are different points of view for the modifications role of Sb in Al-Si alloys, This paper describes the effect of adding Sb on the crystalline process and topography of eutectic Si and the trail of Sb was studied in this paper. It is also compared with adding Na. The results show that the eutectic state changes after adding Sb and an AlSb compound appears in the Si phases, The role of Sb is to separate dispersed crystals of AlSb from the melt and these dispersed crystals are heterogeneous nucleus of Si.