[en] Highlights: • The nano-modification of a healing agent for vascular self-repairing fiber reinforced composites via CNTs was studied • The dynamic viscosity of the healing agents was assessed at different filler loadings • Healing efficiency of the system was evaluated in terms of interlaminar fracture toughness • The nanoreinforcement of the healing agent resulted in significant fracture toughness and healing efficiency improvements • Scanning Electron Microscopy revealed additional energy consumption mechanisms for the reinforced healing agents In this study, the nano-reinforcement of an epoxy healing agent for vascular self-repairing fiber reinforced composites, is explored for the first time. Multi Wall Carbon Nanotubes (MWCNTs) have been selected, as the nanoscaled reinforcing phase of a low-viscosity epoxy healing agent, in three different weight contents. The rheological behavior of the nanomodified epoxies was evaluated via apparent dynamic viscosity measurements and adjusted accordingly. The resulted nanocomposites were infused via a vascular network, to Double Cantilever Beam (DCB) fractured Glass Fiber Reinforced Composites (GFRPs) specimens in order to assess the effect of the MWCNTs on the healing efficiency (η), in terms of maximum bearing load and interlaminar fracture toughness (G_Ic) recovery. The employment of the nanoenhanced healing agent increased the calculated healing efficiency (n_GIc) up to circa 190%, through the introduction of additional energy consumption mechanisms that were confirmed via a comparative Scanning Electron Microscopy (SEM) study.