Abstract: The samples of Al-40Cu alloys with the different contents of rare earth element Er were prepared. The influence of Er on as-cast microstructure of hypereutectic Al-40Cu alloy was investigated by OM, SEM, EDS, XRD, DSC. The results show that the Al₂Cu primary phase in the Al-40Cu alloy can be refined effectively by adding Er. When the addition of Er element is 0.7 wt% in Al-40Cu alloy, the volume fraction of Al₂Cu primary phase is obviously reduced, and the morphology is refined from thick needle flake to irregular granular. When 1.5% Er element is added to the Al-40Cu alloy, the Al₂Cu primary phase changes from needle sheet to block without obvious change in size, compared with that of Al-40Cu alloy. At the same time, a large amount of Al₈Cu₄Er phases are generated. The precipitation temperature of the phase is about 730℃, which is formed before precipitation of the primary phase Al₂Cu. The Al₈Cu₄Er phase participates, and the peritectic-eutectic transformation occurs during the following solidification process and more eutectic is formed based on Al8Cu4Er phase, which increases the volume fraction of the eutectic.