The effects of squeeze casting process on the microstructure and mechanical properties of hypereutectic Al-Si alloy have been studied. The effect of T6 heat treatment has also been examined. The mold for indirect squeeze casting was designed to fabricate 15ø and 25ø specimens and the 50ø specimen was fabricated by direct squeeze casting. The measured cooling rates during solidification of 50ø, 25ø and 15ø specimens are about 36℃ /sec., 88℃/sec. and 106℃/sec., respectively. There were no clear difference in size and distribution of primary Si particles of the A390 alloy modified at 850℃ with P(Cu-P) additions in 15ø and 25ø, 50ø squeeze cast specimens. However, the size and distribution of primary Si particles of the A390 alloy modified at 800℃ were found to be affected by cooling rates during solidification. A further important observation was that eutectic structure was greatly refined by pressure application during solidification and the eutectic Si of 15ø specimen was finer than that of 25ø and 50ø specimens. Due to the microstructural refinement, mechanical properties of 15ø specimen were found to be better than those of 25ø and 50ø ones. After T6 heat treatment, the mechanical properties were remarkably improved.