The paper presents the results of an investigation on aluminum-silicon (LM6) alloy using pressurized lost foam casting process. The study investigated the effect of pressure on casting integrity-geometry, eutectic silicon spacing, particle roundness and hardness. Following air pressures: 1bar, 2bar, 3bar and 4bar were applied on the solidifying alloy. The eutectic silicon spacing and particle roundness were measured using optical microscope which was equipped with image analyzer by averaging of at least ten results as well as Vickers hardness testing machine. For casting integrity-geometry all surfaces of solidified castings were captured by digital camera for better observation. The results show that applying pressure during solidification of the LM6 alloy has significant influence on casting integrity-geometry, eutectic silicon spacing, particle roundness and hardness of the alloy. By increasing the applied pressure, solidification time decline. Consequently, silicon spacing reduces as well as increasing of hardness. Besides, rising air pressure lead to fulfilling of molten which improves the casting integrity and particle roundness.