<p>Graphene oxide (GO) has emerged as ideal reinforced nanofillers in epoxy-based composites, but suffering from poor dispersion because of its high hydrophilicity, and poor compatibility with polymeric matrix which hinders its further application. In this study, a novel tertiary amine-containing compound (C-DEA) was synthesized by the reaction of diethanolamine with C12-C14 alkyl glycidyl ether, then C-DEA was used to modify GO by ionic interaction, thus GO-CDEA was obtained. Moreover, the effect of GO-CDEA content on mechanical and thermal properties of cashew phenol epoxy composite were investigated. Compared to pure epoxy resin (EP), the cashew nut phenol-based nanocomposites (0.2% (by weight) GO-CDEA) perform exceptionally excellent mechanical properties: the rupture strength is 13.76 MPa (73% higher than EP), the Young's modulus is 1049.38 MPa (201% higher than EP), and the elongation-at-break is 138.14% (145% higher than EP). The improved mechanical properties are attributed to the synergistic effect of C-DEA and well-dispersed GO nanosheets, which not only increased the crosslinking density, but also impeded the extension of cracks. Additionally, this novel GO-CDEA-reinforced bio-based renewable cashew phenol epoxy proves to be an ideal candidate for toughening epoxy-based thermosetting materials, showcasing the potential application of bio-based epoxy composite materials.</p> Graphical abstract <p></p>