In this study, we investigated the effects of a small addition of Cu (0.1%) or Ge (0.1%) on the microstructure and mechanical property of AI-Si alloys. The results are as follows. The size of precipitates in the Cu-added or Ge-added alloys is smaller than that in the binary alloy. The size of the precipitates at the grain boundary in the Cu-added or Ge-added alloys is larger than the size of the precipitates in the binary alloy. However, the number of the precipitates at the grain boundary in the Cu-added and Ge-added alloys is smaller than that in the binary alloy. It was found that a small addition of Cu or Ge has the effect of raising the fatigue strength under repeated tensile loading as well as the tensile strength.