In this study, microstructure and mechanical properties of modified (Al10Sr) and grain refined (Al5TiB) A356 aluminum alloy were investigated. To determine the effect of modification and grain refining on the microstructure and mechanical properties of A356 alloy, density measurement, optical microscope and scanning electron microscope examinations and tensile tests were performed. As a result of the study, the highest density and the least percentage of porosity were measured for the modified (with Al10Sr) and grain refined (with 1.5% Al5TiB) alloy system. The lowest density values and the highest percentage of porosity were measured for the unmodified and non-grain refined alloy. According to the tensile tests, average ultimate tensile strength and the highest elongation were obtained for the alloy modified with Al10Sr and grain refined with 1.5% Al5TiB alloy. It was determined that average ultimate tensile strength and percentage of elongation increased as the amount of Al5TiB added for grain refinement and modified to A356 alloy increased.