Some commercial Mg components have been die cast at various casting conditions. The influence of process parameter settings on the microstructural features as well as one kind of defect called segregation band defect were investigated. It was found that more pre-solidified crystals were formed in the condition of lower casting temperature, and more broken dendrites and spherical crystals were formed under higher injection speed. The distribution characters of pre-solidified crystals were also presented and discussed in this paper. Concerning the band defects formed during die casting, a variety of segregation band morphologies as well as the influence of various casting conditions the performances on bands was presented. It was found out that intensification pressure has the strongest effect on the performance of segregation bands inside the castings.