Abstract: Al-Cu-Mg-Ag based alloys with different Er contents had been investigated using mechanical properties testing,x-ray diffraction (XRD),and microstructure observation.It has been shown that adding 0.2 wt%Er refined the grains and increased the mechanical properties of as-cast alloys at room temperature and high temperature.However,Er addition decreased the density of Ω phase after peak aging at 185 ℃,and so decreased the aging hardness and tensile properties of the extruded alloys,which was caused by the formation of Al8Cu4Er compound.