Abstract In this study, the effects of mould materials on microstructure and mechanical properties of cast A356 Al alloy were investigated. The alloy was poured into three different moulds. Then the samples were homogenised and applied T6 heat treatment. The optical, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) studies were made. Secondary dendrite arm spacing (SDAS) was measured by image analysis systems. Hardness and tensile tests were also performed. The ultimate tensile strength (UTS) values were evaluated by Weibull statistical analysis As a result of the studies, the highest values of SDAS were measured for the samples obtained using ceramic mould, which led to the slowest cooling rate, the lowest values of SDAS were measured for the samples obtained using chromite sand mould, which led to the highest cooling rate. The hardness values were increased about 2.5 times which samples were applied T6 heat treatment. The highest tensile strength was observed for the samples obtained using sand mould.