The main objective of this research centered on investigating the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical and thermal properties of curauá-fiber-reinforced composites. The MWCNTs were added either to the fiber surface or into the resin matrix as the second reinforcing phase. The MWCNT-modified curauá fibers as well as raw fibers were characterized using a single-fiber tensile test, TGA, and FTIR analysis. Further, different composite samples, namely, pure curauá, (curauá + MWCNTs) + resin and curauá+ (resin + MWCNTs), were manufactured via compression molding and tested to determine their mechanical and thermal properties. Scanning electron microscopy (SEM) analysis was used to examine the surfaces of the tested fibers. It was found that the addition of MWCNTs to the curauá fibers resulted in positive effects (an enhancement in properties was found for the MWCNT-modified fibers and their composites). The addition of MWCNTs also increased the thermal stability of the natural fibers and composites.