Natural fiber-reinforced composites have become superior materials due to their potential to replace synthetic fibers, because of their low density, lightweight, low-cost biodegradability, and high specific strength. This study finds out the mechanical properties of coir fiber-reinforced polyester matrix composites with the addition of filler content. The composites were fabricated using a compression molding machine with a dimension of (300x300x3) mm. Totally 6 laminates were fabricated with variations in fiber and filler content. The fabricated composites were cut the different types of ASTM standards. The mechanical properties of the calcium carbonate and groundnut shell-filler added coconut fiber- reinforced polyester composites were studied. The maximum tensile, flexural, and impact strength was achieved by 29.6 MPa, 56.8 MPa, and 34.8 kJ/m2 respectively. The addition of fillers in composite increases the mechanical strength. Fractography studies were used to analyze the fracture behaviour in fiber-reinforced composites. Coir fiber-reinforced composite materials are applicable for low load-bearing applications