- Abstract The extraordinary mechanical properties of graphene prompt its incorporation into a wide range of polymeric nanocomposite materials (NCMs). However, similar to other nanomaterials (NMs), the reinforcement efficiency of graphene and its derivatives is hindered by their agglomeration and poor compatibility with the polymer matrix. In this paper, edge-functionalized graphene nanoribbons (EF-GNR) are incorporated in brittle epoxy polymer matrix. The functionalization process by polyvinylamine (PVAM) chains occurs only at the edges, preserving the in-plane sp 2 of the graphene; thereby the PVAM EF-GNRs are both compatible and strong. The produced NCMs exhibit a wide range of enhanced mechanical properties including fracture toughness, flexural strength and shear strength at low EF-GNR loading (0.15 wt%). The effect of the edge functionalization is indeed critical, demonstrating superior mechanical properties by the EF-GNR loaded NCMs compared to pristine-GNR loaded composites. Finally, a comparative overview of various carbon NM-loaded NCMs indicates that EF-GNR possess high reinforcement efficiency (enhancement % per NM loading %) making it an attractive filler for polymer systems.