The effects of melt holding time and various melt treatment conditions such as phosphorus treatment, simultaneous treatment after remelting of phosphorus treated alloy, and strontium treatment one hour after phosphorus treatment on the simultaneous refinement of primary and eutectic silicon in hypereutectic Al-Si alloy were studied. In case of simultaneous treatment with 0.04%P and 0.05%Sr, the size of primary silicon particles increased with melt holding time and started to decrease after one hour and modified microstructure was maintained during melt holding time for four hours. In case of strontium treatment after remelting of phosphorus treated alloy, the size of primary silicon particles increased with melt holding time and started to decrease after 30 minutes and eutectic Si modification was achieved during melt holding time for four hours. Strontium treatment after remelting of phosphorus treated alloy showed the smallest primary Si particle size among the melt treatment conditions.