Magnesium alloys are becoming more and more attractive because of their low density, high specific stiffness and strength, good heat conductivity, high electromagnetic interference shielding and damping capabilities, etc. Magnesium alloy components produced by semi-solid processing (SSP) has the merits of high dimension stability and quality. Moreover, it is desirable to apply the SSP technology to produce components free of gas holes and porosity which are usually found in those produced by the die casting. SSP of magnesium alloys has been utilized in Japan and Taiwan, China. In this paper, preparing methods of semi solid slurry appropriate for magnesium alloys are introduced, including stirring, SSIT-semi solid isothermal heat treatment, pouring temperature controlling, grain refinement and so on. The effects of process parameters on the microstructure of semi-solid slurry are also discussed. In addition, thixomolding technology practically utilized in the semi-solid processing of magnesium alloys is also introduced. At last the prospect of Semi-solid processing technologies for magnesium alloys are discussed.