Influence of alloy purity on the tensile properties of Al-Si eutectic alloy castings has been investigated by using two kinds of the melted alloys: L-Alloy of 99.89 mass% purity and H-Alloy of 99.98 mass% purity. Although the base structure in both of alloys was composed of proeutectic alpha-phase and eutectic structure, the eutectic structure of H-Alloy was finer than that of L-Alloy. Coarse crystals of plate-like silicon were observed in L-Alloy, while were not observed in H-Alloy. Based on the results of Brinell Hardness Test on the solidification structure, it was found that there was little difference of the hardness between the both alloys. Tensile tests were also performed in an atmosphere at room temperature. The elongation of H-Alloy was twice as large as that of L-Alloy, though the tensile strength of L-Alloy and H-Alloy were almost the same.