This study aims to investigate the influence of intermetallics morphological modification on mechanical properties of iron-containing Al-Si-Mg casting alloys. The modification of the intermetallics was performed by using melt-shearing treatment prior to commercial high pressure die casting. The process parameters of the melt-shearing treatment were controlled and optimized based on the theoretical consideration of the intermetallics formation behavior. It was found that the mechanical properties of low-iron containing Al-Si-Mg alloy was improved due to the modification of primary α-Al from dendritic to globular form by the melt-shearing. Regarding to high-iron containing Al-Si-Mg alloy, harmful morphology of intermetallics was successfully modified by the melt-shearing at semi-solid region, which results in the improvement of mechanical properties such as elongation.