Abstract: This study systematically investigates the effects of hot isostatic pressing (HIP) post-treatment on the microstructure and mechanical properties of selective laser melting (SLM)-fabricated FeNiCrMnAl high-entropy alloy. The work aims to characterize HIP-induced microstructural changes and evaluate their influence on mechanical performance under both room temperature and elevated-temperature (300 ℃) conditions. The FeNiCrMnAl high-entropy alloy was fabricated using SLM technology. HIP treatment was subsequently applied to the as-built samples. Microstructural characterization was performed to analyze phase composition, grain morphology, and defect distribution. Mechanical properties were evaluated through tensile testing at room temperature and 300 ℃. Fracture surfaces were examined to determine failure mechanisms. HIP treatment effectively reduces void defects and improves densification in the SLM-fabricated alloy. The primary alloy phases and melt pool morphology remain unchanged after HIP processing. However, microstructural modifications occur, including grain coarsening and an increased proportion of low-angle grain boundaries. These changes lead to improved ductility, with the HIP-treated alloy exhibiting enhanced elongation compared to the as-built material. The fracture mechanism transitions from a mixed quasi-cleavage and ductile mode to predominantly ductile characteristics. The application of HIP post-processing to SLM-produced FeNiCrMnAl high-entropy alloy demonstrates significant benefits for mechanical performance. While preserving the primary phase composition, HIP treatment modifies the microstructure to enhance ductility and alter fracture behavior. These findings provide fundamental insights into the use of HIP technology for optimizing additively manufactured metallic components. The study establishes that HIP can effectively improve the properties of SLM-fabricated high-entropy alloys without altering their fundamental phase characteristics.