Microstructure and tensile properties of as-cast and T6-treated Al-4%Cu-3%Si alloy with different applied solidification pressures were investigated. The pressure has significant effect on the formed microstructure. It is observed that as the pressures increase, the porosities were removed, and the size and the secondary dendrite arm spacing of primary α-Al grains decreased evidently, and the morphology of eutectic Si particles changed from long acicular to small granular type. Hence, the tensile properties of the alloy were improved. The research has shown that the aspect ratio (A.R.) of the Si particles decreased after the solution and aging treatment. The A.R of the Si particles in the alloys with applied solidification pressure decreased more remarkably and this indicated that the Si particles can be more prone to be dissolved into α-Al matrix. Thus, the increase of the elongation was achieved.