Squeeze casting is a process in which a high external pressure is applied and maintained on the molten metal from the start to the end of solidification. Solidification of metal under pressure decreases the porosity, increases the solidification rate and improves the mechanical properties of the castings. In this research, the effects of pressure, casting temperature, casting section thickness and silicon content on the structure and properties of a squeeze cast hyper-eutectic gray cast iron were investigated. The results indicated that application of pressure during solidification resulted in a decrease in the amount of graphite formed, reduction in the graphite size, decrease in the ferrite content and increase in the pearlite and D type graphite formed in the microstructure. Increasing the casting temperature, casting section thickness or silicon content of the alloy resulted in increasing the amount and size of the graphite flakes formed, decreasing the pearlite content, increasing the ferrite content and decreasing the D type graphite. The average graphite content of the castings was decreased from 13.37 percent for the sample cast under atmospheric pressure to 9.15 percent for the sample squeeze cast under 75 MPa. The average length of flake graphites was increased from 8.4 to 10µm when the casting temperature was increased from 1170 to 1230°C under an applied pressure of 50 MPa. With application of pressure on the melt, some graphite particles with spherical or compacted shapes were observed in the microstructure. The tensile strength and hardness of the castings were increased from 162.8 MPa and 230 HBN to 273.5 MPa and 260 HBN, respectively, when the applied pressure was increased from atmospheric pressure to 75 MPa. The impact energy and elongation of the castings were increased from 2.05 J and 2.5 percent to 2.4 J and 5.7 percent, respectively, when the applied pressure was increased from atmospheric pressure to 75 MPa. Increasing the casting temperature, casting section thickness and silicon content of the melt resulted in lower tensile strength and hardness and improved elongation and impact energy. The density of the castings was increased with increasing the applied pressure or decreasing the casting temperature, casting section thickness or silicon content of the melt.