Abstract: The electron microprobe was used to determine the solute distribution coefficient at liquid-solid interface in Al-1.35%Cu and Al-0.25%Cr alloys during directionally solidification.It has been shown that the content of Cu decreased exponentially in liquid zone and linearly in solid zone with the distance from the interface.The thickness of the liquid-solid interface is about 5～7μm,the larger is the solidification rate,the shorter is the initial transition zone of solidifition.For Al-1.35%Cu alloy,the equilibrium solute distribution coefficient k₀ less than 1 and its non-equilibrium solute distribution coefficient k is larger than k₀.For Al-0.25%Cr,k₀ is more than 1 and k is less than k₀.The difference between k and k₀ is greatly increased with the increase of the solidfication rate.