<p>This research explores the optimization of mechanical properties of the Nylon-Glass Fiber composites manufactured by Selective Laser Sintering (SLS) under varying annealing conditions. Nylon 12, which is reinforced with glass fibers, was fabricated by SLS process, after which annealing at room temperature, 110, 130, and 150&#xa0;°C was done. The effects of these thermal treatments had made changes on the composite’s mechanical properties like tensile, flexural, and impact properties which were then evaluated. Metallurgical tests such as Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM) were employed to understand the microstructural changes that had happened due to annealing and to identify the reasons for the property enhancements. Results revealed a significant improvement in mechanical performance, particularly at 150&#xa0;°C, where the composites exhibited superior tensile, flexural, and impact strength due to its lesser structural defects, improved polymer chain alignment, and upgraded fiber-matrix bonding. However, further increases in temperature led to poor performance, bringing into view the critical importance of precise annealing parameters to get the best results. FTIR analysis confirmed the rearrangement of the polymer chains and reduced chemical degradation after annealing, while FE-SEM images showed improved inter-molecular bonding and a more homogeneous microstructure. These findings bring into a conclusion the potential of controlled annealing processes to significantly enhance the durability, strength, and resilience of SLS-printed composites, making them particularly suitable for demanding applications in the aerospace, automotive, and industrial manufacturing sectors. This study provides a comprehensive framework for tailoring composite properties through post-processing, thereby advancing the capabilities and industrial relevance of additive manufacturing technologies.</p>