The effects of rare earth samarium （Sm） additions on the microstructure and mechanical properties of as-cast Al-Si-Cu alloy were investigated by optical microscopy and scanning electron microscopy （SEM）. The results show that Sm can effectively refine the a（Al） dendrite and the eutectic silicon. In addition, the shape of iron-rich phases changes from the Chinese script-like to slender-like ones and the volume fraction of iron-rich phases is decreased by the addition of Sm. Two kinds of Sm-rich interrnetallics are found： AlSiSm and AlSiCuSm. The plate-like AlSiCuSm phase always associates with the needle-like AISiSm phase. The mechanical properties are improved by the addition of Sm, and the good ultimate tensile strength （220 MPa） and elongation （3. 1%） are obtained from the Al-Si-Cu-1.0Sin alloy.
