Formation of oxide inclusions in the molten aluminium alloys during solidification is investigated. The oxidation tendency of both Al-4.5wt%Cu and Al-7wt%Si alloys is increased with melt temperature, particularly over 700˚C. However, an Al-5wt%Mg alloy exhibits a decreasing mode over 800˚C. The oxidation behavior with holding time shows the S curve shape for all of the alloys. It is shown that the mechanism of oxidation of Al-5wt%Mg alloy has a two step process different from that of Al-4.5wt%Cu and Al-7wt%Si alloys. The species and morphology of oxide inclusions in each alloy is also shown. The microstructure was more coarsened during solidification when the melt contains a large amount of oxide inclusion than when it doesn`t. This result can be explained in terms of both the hindrance of heat extraction by oxide film formed on the aluminium melt and the difference of heat capacity between the aluminium melt and oxide inclusion during solidification. (Received March 2, 1998)