Mechanical property characterization including bending, tensile, and fracture properties for a new functionalized nanofiber/epoxy composite were conducted. Results show that there was only very little increase in mechanical properties of nanocomposites although we used GCNF-ODA reactive linkers to improve the interface. The interfacial stress level of nanocomposites should be much higher than that of traditional composites because of high property mismatch between the nanoscale reinforcement and the matrix. In order to design strong and stiff nanocomposite materials, one should use aligned nanofibers with a relatively large volume or weight fraction. Also, the length of the nanofiber should be long enough and its diameter not very small in order to facilitate the interfacial load transfer mechanism.