Most of the work reported at this conference concerned the semi-solid processing of low melting point alloys, and in particular light alloys of aluminum and magnesium. Mg alloys are very attractive as structural materials, because they are the lightest metal among all structural metal materials and excellent specific strength. The purpose of this paper is to develop a semi-solid microstructure of Mg alloys using electromagnetic stirring applicable for lighter automobile. The size of primary solid particle and the degree of sphericity as a function of the variation in cooling rate, stirring speed, and holding time were observed. By applying electromagnetic stirring, primary solid particles became finer and rounder relative to as-cast sample. As the input Hz increased from 10Hz to 14Hz, particle size decreased. The size of primary solid particle was found to be decreased with increasing cooling rate. Also, it decreased with stirring up to 3 minutes but increased above that point. The degree of sphericity became closer to be 1 with hold time. Semi-solid microstructure of Mg alloys, one of the low melting point alloys, could be controlled by electromagnetic stirring.