Polyethylene glycol (PEG) was successfully grafted onto the surface of graphene oxide (GO) by the "grafting to" technique. PEG, GO as well as the PEG grafted GO (GO-g-PEG) was successfully incorporated into an epoxy matrix and subsequently cured using diethylenetoluenediamine (DETDA) to make epoxy nanocomposites. Mechanical, thermal, and rheological properties of the epoxy nanocomposites were studied to check the effectiveness of these fillers in the epoxy matrix. An improvement of 255% and 334% at a very low filler loading of about 0.1 wt% was observed in the fracture toughness of GO and GO-g-PEG loaded systems versus the neat epoxy. Toughening mechanisms are also explained by analyzing SEM images of the fractured surface. Modeling of rheological properties was carried out by following time-independent Newtonian model. The homogeneity of the epoxy filler systems are explained with the help of Cole-Cole plots. The thermal stability of the filler loaded epoxy composites was examined in detail by TGA. Improvements in mechanical properties reveal the potential benefit of the grafting process in epoxy toughening. POLYM. ENG. SCI., 2020. (c) 2020 Society of Plastics Engineers