The purpose of this study is to investigate the influence of samarium addition on the microstructures and mechanical properties of Al-5Cu alloys. The microstructures were examined by optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectroscopy and differential thermal analysis. It was found that Sm was capable significantly of affecting the microstructures of Al-5Cu alloys. When 0.4 wt% Sm was added into the alloy, the aspect ratio and the mean area of Al_2Cu phase were 10.9 and 61.0 μm2. They were decreased by 31.5% and 43.3% when compared with unmodified alloy. Meanwhile, a kind of nano size strengthening Al2 Sm phase was formed in Al-5Cu alloys. In addition, the differential thermal analysis results showed that Sm addition results in a decrease in the melting temperature of α-Al and Al_2Cu. And a good combination of yield strength(244.5 MPa), ultimate tensile strength(269.4 MPa) and elongation(6.9%) was obtained when the Sm addition was 0.4 wt%. Compared with unmodified Al-5Cu alloys, they were increased by 37.6%, 35.2% and 21.1%, respectively. The purpose of this study is to investigate the influence of samarium addition on the microstructures and mechanical properties of Al-5 Cu alloys. The microstructures were examined by optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectroscopy and differential thermal analysis. It was found that Sm was capable of significantly affecting the microstructures of Al-5Cu alloys. When 0.4 wt% Sm was added into the alloy, the aspect ratio and the mean area of ​​Al 2 Cu phases were 10.9 and 61.0 μm 2. They were decreased by 31.5 % and 43.3% when compared with unmodified alloy. However, a kind of nano size strengthening Al2 Sm phase was formed in Al-5Cu alloys. In addition, the differential thermal analysis results showed that addition result in a decrease in the melting temperature of α-Al and Al 2 Cu. And a good combination of yield strength (244.5 MPa), ultimate tensile strength (269.4 MPa) and elongation (6.9%) was obtained when Sm addition was 0.4 wt%. Compared with unmodified Al-5Cu alloys, they were increased by 37.6%, 35.2% and 21.1%, respectively.