In the present work, the effects of applied pressure during solidification on microstructure and mechanical properties of a hypereutectic ductile iron were investigated . The suitable chemical composition of the base cast iron (3.65 wt%C, 2.24 wt%Si and 4.4 wt%C.E.) to avoid excessive carbide formation in the microstructures was determined after some preliminary test. Also the close lid ladle nodulizing treatment was recognized as the suitable nodulizing method for treating small quantities (about 5Kg) of cast iron. Furthermore, effects of some of the nodulizing treatment parameters on the microstructures were examined and 1400°C, 3wt% addition and 20 seconds were chosen as suitable processing values for nodulizing temperature, amount of nodulizing agent addition and delay time between nodulization and pouring, respectively. Consequently, magnesium treated melts were squeeze cast under external pressures of up to 75MPa using a hydraulic press and their microstructural and mechanical characteristics were investigated. Microstructural measurements were carried out on un-etched and etched surfaces of the castings using an optical microscope and Clemex image analysis software. Results showed that pressurized solidification of ductile iron had a significant effect on its microstructure and especially on the characteristics of the graphite nodules. Increasing the applied pressure from zero to 75Mpa decreased the amount of free graphite observed in the microstructures, reduced the nodule size and increased the graphite nodule count and graphite nodules sphericity. Increasing of the applied pressure also resulted in higher pearlite and cementite and lower ferrite contents in the microstructures. Moreover, the ultimate strength, yield strength and fracture toughness of the castings improved as the applied pressure rose from zero to 50MPa. Further increase in the applied pressure resulted in slightly lower mechanical properties. SEM fractographs showed an increasing trend for ductility of the fractured surface with increasing the applied pressure up to 50MPa followed by a decrease as the pressure was further increased to 75MPa. The reduction in the mechanical properties at the highest applied pressures was associated with the influence of the applied pressure on the formation of more carbide phase and decrease in the graphite nodule cont in the microstructures.