The article focuses on examining of the microstructure and mechanical properties of the castings from AIMg3 alloy. Examination were subjected molds for pressing a tire, which are produced by low-pressure casting technology. Analysis of the microstructure by optical microscopy was used in the research. Structural components of alloy were analyzed in detail by means of electron microscopy (SEM) and EDX analysis. Investigation of mechanical properties was performed by a static tensile test and measurement of Brinell hardness. Static tensile test was performed by normal and increased temperature for simulation of mold working conditions.