Abstract: This study aims to systematically investigate the influence of different solution heat treatment temperatures on the microstructure and mechanical properties of GH4169 alloy fabricated by selective laser melting (SLM), in order to optimize its heat treatment process. After homogenization, SLM-formed GH4169 alloy specimens were subjected to solution treatments at T1°C, T2°C, T3°C, and T4°C (where T1 < T2 < T3 < T4), followed by standard aging treatment. The microstructures under different conditions were observed, macro-hardness was measured, and the transverse and longitudinal room-temperature tensile properties of the specimens treated at the lowest (T1°C) and highest (T4°C) solution temperatures were analyzed in detail. Microstructural results revealed that with increasing solution temperature, the amount of δ-phase in the alloy decreased significantly, transitioning from a continuous distribution to a discontinuous, dot-like morphology. Hardness measurements indicated minor fluctuations in hardness values (HRC 44.5–HRC 46.7) across specimens treated at different solution temperatures, without a clear observable trend. Mechanical property results showed that while a higher solution temperature (T4°C) led to a slight reduction in strength, it significantly improved the plasticity of the alloy in both transverse and longitudinal directions. Solution heat treatment temperature is a critical parameter for controlling the microstructure of SLM-formed GH4169 alloy, particularly the characteristics of the δ-phase. By employing a higher solution temperature (T4°C), excessive continuous δ-phase can be effectively dissolved, thereby substantially enhancing the plasticity and toughness of the alloy while maintaining relatively high strength. This finding provides important guidance for optimizing the overall mechanical properties of SLM-formed GH4169 alloy.