It is of importance to investigate different strategies to improve the poor fracture toughness of epoxies, which are widespread polymeric matrices in composites. In this study, different PA66 nanofiber yarn contents (0.5, 1 and 3 wt%) were used to improve the fracture toughness of the epoxy-based nanocomposite. Fracture toughness was measured using the single edge notched bend (SENB) test. Results showed that by increasing the nanofiber yarn content in the epoxy, the elastic, plastic and the total works as well as the maximum load related to the initiation of crack propagation were improved. Roughness, plastic deformation and interfacial adhesion were investigated via SEM images. (C) 2017 Elsevier Ltd. All rights reserved.