The adiabatic shear behaviour of aluminum-scandium(Al-Sc) alloy under high strain rates ranging from 3.0×105 s-1 to 6.3×l05 s-1 is studied by using a compressive-type split-Hopkinson pressure bar (SHPB). The results show that both the shear stress and the strain rate sensitivity increase with increasing the strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. At a strain rate of 3.0×105 s-1, the fracture surface is characterised by multiple transgranular cleavage fractures. However, for strain rates greater than 4.5X×105 s1, the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the duetility of the unweldable Al-Sc alloy improves with increasing the strain rate.