The modifying effects of a new type of Al-P master alloy on eutectic and hyper-eutectic Al-Si alloys were investigated. It is found that excellent modifying effect on these alloys can been obtained by adding the new type of Al-P master alloy. It is also found that the modifying efficiency of the Al-P master alloy can be improved by the addition of Al-8Ti-2C master alloy to the Al-Si melt. When the content of TiC particles (by Al-8Ti-2C master alloy) in the Al-24Si melt is 0.03%, the average and largest grain size of primary Si can be decreased to 41 m, 55 m from the original 47 m and 75 m. The modifying effect occurs after 50 minutes from adding the Al-P master alloy and the TiC particles, and remains steady with the increase in holding time. The average grain size of the primary Si can be decreased to 30 m from 50 m when the content of TiC particles in Al-12Si melt is 0.03%.