The effects of small addition of scandium on the microstructure and ageing characteristics in Al-2.5Cu-1.5Mg alloys have been investigated. The results indicate that the age hardening response of the Al-2.5Cu-1.5Mg alloy can be enhanced while the general form of the ageing curve is not altered by small addition of Sc. TEM observations show that GPB can only precipitated during the second age hardening period which will make a great contribution to the age hardening, and the morphology of GPB can be modified by the small addition of Sc, which does result in a refinement of the distribution of GPB in Al-2.5Cu-1.5Mg-0.2Sc.