The effects of carbon nanotubes (CNTs) on the mechanical and fracture properties of ramie fiber-reinforced epoxy composites were investigated. Three-point bending, short beam shear, single-edge-notch bending, and Charpy impact tests were employed to evaluate the properties of ramie fiber-reinforced composites without and with CNTs modification. The fracture mechanisms were revealed with the aid of the dynamic mechanical analysis, Fourier transform infrared, and X-ray photoelectron spectroscopy. It was found that the mechanical and fracture properties of ramie fiber-reinforced composites were enhanced by incorporating multiwalled carbon nanotubes, except the impact fracture toughness. The unique chemical compositions and the multiscaled nanosized microstructures of natural fibers brought into focus new mechanisms for the improvement of the mechanical properties of natural fiber-reinforced composites.