Al–Fe–Mn alloys are widely preferred in packaging, automotive, and heat exchanger applications due to their high corrosion resistance, good formability, and thermal stability. The addition of rare earth elements to the aluminum matrix enhances the microstructure through mechanisms such as grain refinement, modification of intermetallic phases, and improved matrix stability, thereby increasing the mechanical and functional performance of the alloys. In this study, the effect of Sm addition on the microstructural properties of the Al–Fe–Mn alloy was investigated. For this purpose, alloys containing 0, 0.2, 0.4, and 0.6 wt.% Sm were produced by melting and casting, followed by homogenization heat treatment. After homogenization, the samples were prepared metallographically and characterized using optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX). In order to determine the effect of Sm addition on the hardness of the alloy, comparative hardness measurements were carried out on the samples. The results revealed that increasing Sm content weakened the eutectic structure, significantly refined the grain size, and led to a more uniform distribution of Fe-based intermetallic phases. Furthermore, the formation of Sm–Fe intermetallic phases (Sm₂Fe, Sm₃Fe, Sm₅Fe) contributed to an increase in hardness values.