Compositional variations of magnesium alloys AZ91D and AM60B in a crucible during hot-chamber die casting process have been investigated. The sampling of molten metal for chemical composition analysis was carried out at three positions (A: bottom, B and C: 100 and 300 mm upside from the bottom, respectively) within a crucible of 600 mm in depth. The picked molten metal was poured into a steel mold to cast into a rod 40mm diameter and 120mm length. Results show that heavier elements such as Al, Zn, Mn, Fe, etc. were concentrated at the bottom of crucible, which is resulted from long-time, repeated casting operations without bailing out. The macro segregation of alloying elements and impurities are partly caused by the reaction between the alloying elements. Short-periods of holding time up to 250 minutes, however, did not significantly change the concentration of Al and Zn at the entrance of gooseneck.