In this work, a facile in situ polymerization method was developed for the preparation of polyamide 6 (PA6) chains grafted graphene oxides (GO). Based on ethanolic solution precipitation method, the powders of PA6, PA6/GO-0.5 and PA6/GO-1.0 were fabricated and dispersed uniformly into epoxy resins at varying loadings. The surface modification of GO and mechanical properties of epoxy composites were investigated systematically. The mechanical tests indicate that, without impairing tensile properties and glass transition temperature , the fracture toughness of PA6/GO-1.0 particles reinforced epoxy composites exhibits a 52.6% increase compared with neat epoxy at 1.5 wt% loading. Based on adequate fractographic study, the excellent toughening effect of PA6/GO-1.0 can be attributed to the better particle/matrix interface, rougher interface with small convex structures and more energy consumption of particle fracturing, which are resulted from the existence of PA6 chains grafted GO nanosheets . Moreover, the addition of GO and PA6 is 0.015 and 1.5 wt% respectively for the maximum fracture toughness value in this work. The dosage is very small compared with epoxy reinforced with GO or PA6 separately, giving an economically feasible method for the toughening of epoxy resin.