<jats:p>In this work, we present a new criterion, unlike other attempts, to evaluate and quantify the degree of damage of composite material when it subjected to a sudden impact load. Our criterion exploits the high intrinsic electrical conductivity property of the Multi-walled carbon nanotubes (MWCNTs) after dispersing different concentrations of them (0, 0.5, 1.0, 1.5 and 2.0 %) in the epoxy matrix of a glass fibre composite. Following this goal, the low-velocity impact and flexural after impact (FAI) tests on the MWCNTs-glass epoxy (i.e. MWCNTs-GF) nanocomposite were evaluated. At the same time, the changes in its electrical resistance were measured. The results showed that the properties of the self-sensing composites were significantly affected by impact energy. The damage after impact causes an increase in the electrical resistance of the MWCNTs-GF nanocomposite and increases with increased impact energy. In addition, the samples containing a high concentration of MWCNTs showed lower damage sensitivity under all impact energies levels as compared with the samples contain a lower MWCNTs concentration. Therefore, the results presented in this work have shown that it is possible to associate the change in electrical resistance of the MWCNTs-GF nanocomposite with the degree of damages caused by impact load.</jats:p>