When Mg-10(wt.%)Sb alloy was melted, the alloy melt was into two tiers. The semisolid formed in the bottom of the melt became Mg-13Sb alloy and the upper of the melt became Mg-9Sb alloy. Both of Mg-9Sb and Mg-13Sb alloys consist of α-Mg phase and α-Mg3Sb2 precipitates which distributed homogenously in the matrices. In Mg-9Sb alloy, two types of precipitates are observed, the majority rod-shaped and the minority rectangle-shaped. In Mg-13Sb alloy, all of the precipitates were just block.