The paper focuses on the research of the influence of chosen technological parameters of die casting on the selected mechanical properties of castings based on Al-Si alloys. The experiments conducted within the frame of the practical part examined the plunger pressing speed in the mould cavity influencing the mechanical properties of a casting which were represented by ultimate tensile strength and percentage share of porosity of Al-Si castings. Plunger pressing speed is closely related to mould cavity filling mode which affected the final porosity of casting. In the case of increased percentage porosity share, the ultimate tensile strength decrease was detected due to the reduction of the cross-section area of the casting. The increase in percentage porosity share in the casting was caused by the increase in plunger pressing speed. To achieve the desired quality of castings, higher production efficiency, and reduced occurrence of faulty pieces during production, an optimal set of technological parameters of die casting is inevitable.