Laser powder bed fusion (LPBF) process is an Additive Manufacturing (AM) technology that allows the production of complex shaped components in an easier way than traditional ones. The as-fabricated Inconel 625 (IN625) parts by LPBF require post heat treatments to meet the industrial requirements in order to reduce the residual stresses and obtain tailored microstructure. However, it is also fundamental to control the microstructural evolution of the IN625 components owing to the thermal exposure over 500 °C during service, which can have a significant impact on their mechanical properties. This study aims to investigate the influence of prolonged heat treatments on microstructure and mechanical properties of IN625. The prolonged heat-treated IN625 samples are investigated by Optical Microscope (OM), Field Emission Scanning Electron Microscope (FESEM) and X-Ray Diffraction (XRD) analysis, whereas the mechanical properties are evaluated by hardness test.