The design, production, and characterization of coir fiber-reinforced composites employing epoxy resin modified with CNSL are investigated in this work. A 1:1.25 epoxy-to-hardener ratio, 15-20% CNSL, and vacuum bagging were used to create fiber arranged for sun-dried coir composites. Structural and thermal properties were assessed using mechanical tests (tensile, flexural, and impact) as well as FTIR, TGA, and SEM investigations. The findings show that CNSL improved impact resistance and thermal stability, while interlocking coir composites had greater mechanical strength. However, impact hardness was decreased by over-mercerization. The results show that coir fiber composites are environmentally friendly substitutes for construction, automotive, and aerospace applications. To improve performance, future studies can optimize fiber loading and biodegradability.