Rapid solidification of AlSr alloy results in refinement of microstructure, increment of default density, uniformization of composition and supersaturation of solid solution. Twozone microstructures are clearly found in the transverse section of rapidly solidified AlSr ribbons. As a reslut of the high cooling rates （about 106 K/s）, the grain size at the chilled side is up to nanometer level. The modifying experimental results show tha the AlSr master alloys formed at different cooling rate have different modifying effect. To obtain the same modification rating, the additional amount of rapidly solidified AlSr master alloys is decreased by 50%￣60% and the incubation period is reduced by 50% in comparison with normal ingot master alloy.