Epoxies are widely used in many engineering applications, however, their fracture energy remains less than desired and conventional toughening agents usually lead to compromised tensile strength. In this study, a simple one-pot blending method was used, in which both graphene oxide and a block ionomer were blended with epoxy resin. Herein, we reported that increases of ∼200% in fracture energy (GIC), 48% in uniaxial tensile strength (σt) and 340% in tensile strain could be achieved by incorporating 1.0 wt% graphene oxide into an epoxy matrix with 20 wt% sulfonated polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SSEBS). In addition, the glass transition temperature (Tg) of the nanocomposite increased with increasing graphene oxide (GO) content and the storage modulus (E′) decreased when the GO content was less than 0.50 wt% owing to the introduction of the block ionomer SSEBS. Careful examination of the nano-morphology of SSEBS revealed that it improved the dispersion of the graphene oxide in and enhanced its interaction with the epoxy matrix, hence simultaneously strengthening and toughening the epoxy resin.