Hypo- and hyper-eutectic Al-Si alloys were rapidly solidified from the low or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy,and X-ray diffraction methods. The primary silicon in the Al-22(wt pct)Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from high temperature melt had finer Al-rich and Si-rich phase particles in either Al-7(wt pct)Si or Al-18(Wt pct)Si alloy. The mechanism was explained by the nature of the liquid structure Hypo- and hyper-eutectic Al-Si alloys were rapidly solidified from the low or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy, and X-ray The primary silicon in the Al-22 (wt pct) Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from High temperature melt had finer Al-rich and Si-rich phase particles in either Al-7 (wt pct) Si or Al-18 (Wt pct) Si alloy. The mechanism was explained by the nature of the liquid structure