Rapidly solidified hypereutectic Al-21Si was prepared by the single roller melt-spinning technique. The microstructure morphology characteristics and phase structures of the alloy were characterized using SEM, TEM and XRD technique. The results showed that the grains were refined and the micro-nano composite structures were formed under rapid solidification. The microstructure of the Al-21Si alloy was composed of micro-nanostructured α-Al phase and feather-needle-like eutectic α-Al+β-Si phase. The α-Al phase was the leading phase in the eutectic α+Si phase. The nucleation and growth of primary silicon are suppressed and primary silicon could not be precipitated. The hypereutectic Al-21Si alloy showed the hypoeutectic solidification microstructure. Wear resistance was improved obviously when the rapidly solidified and was five times higher than that of the traditional casting alloys.