The study systematically investigated the effects of master alloy addition containing rare earth elements La and Yb on the microstructures characteristic and tensile properties of Al Si10Cu3 alloy. It was studied by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectrum and differential thermal analyzer. The results showed that the addition of(La+Yb) obviously reduced the sizes of the primary α-Al phase and eutectic Si particles as well as β-Al5 Fe Si phase and improved the morphology of the primary α-Al phase and eutectic Si particles. The optimum addition of(La+Yb) addition was 0.6 wt.%. Comparing the 0.6 wt.%(La+Yb) modified Al Si10Cu3 alloy with the unmodified alloy, it was found that the mean diameter, mean area and SADS of primary α-Al phase were decreased by 50.80%, 75.74% and 50.83% respectively; the aspect ratio, size(length) and mean area of eutectic Si particles were decreased by 66.30%, 81.78% and 78.99%, respectively, and the average size of the β-Al5 Fe Si phase was 16.4 μm. In addition, the addition of(La+Yb) greatly improved the tensile properties of Al Si10Cu3 alloy, especially in the ultimate tensile strength and elongation as a result of the significant improvement in microstructure. The study systematically investigating the effects of master alloy addition containing rare earth elements La and Yb on the microstructures characteristic and tensile properties of Al Si 10 Cu 3 alloy. It was studied by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy diffraction spectrum and differential thermal analyzer. The results showed that the addition of (La + Yb) significantly reduced the sizes of the primary α-Al phase and eutectic Si particles as well as β-Al5 Fe Si phase and improved the morphology of the primary α- The optimum addition of (La + Yb) addition was 0.6 wt.%. Comparing the 0.6 wt.% (La + Yb) modified Al Si10 Cu 3 alloy with the unmodified alloy, it was found that the mean diameter the mean area and SADS of primary α-Al phase were decreased by 50.80%, 75.74% and 50.83% respectively; the aspect ratio, size (length) and mean area of ​​eutectic Si particles were decreased by 66.30%, 81.78% and 78.99% , respectively, In addition, the addition of (La + Yb) greatly improved the tensile properties of Al Si 10 Cu 3 alloy, especially in the ultimate tensile strength and elongation as a result of the significant improvement in microstructure.