Influences of the symmetric Stone-Wales (SW) defect on the electronic transport properties of the zigzag graphene nanoribbons (ZGNRs) have been studied using ab initio simulation based on density functional theory (DFT) combined with non-equilibrium Greens function (NEGF) technique. The calculated transmission spectra T (E) at various bias windows, device densities of states (DDOS), current characteristics as well as local density of states (LDOS) of the defective asymmetric and symmetric ZGNRs are presented in comparison with those for the pristine ZGNRs. The metallic character of the electronic transport in both asymmetric and symmetric ZGNRs has been established: the current has a semiconductor behavior, with negative differential resistance (NDR) effect. Symmetric SW defect, as a most unfavorable SW defect type for electric conductance, remarkably reduces the current values, but does not change the character of conductivity in both the asymmetric and symmetric ZGNRs. NDR has been explained by the SW defect-induced alteration of the number of frontier molecular orbitals entering bias windows. density-functional theory, non-equilibrium, Green function, electronic transport, graphene nanoribbon, transmission spectrum, current–voltage characteristics