The graphene nanoribbon (GNR)/carbon composite nanofiber yarns were prepared by electrospinning from poly(acrylonitrile) (PAN) containing graphene oxide nanoribbons (GONRs), and successive twisting and carbonization. The electrospinning process can exert directional shear force coupling with the external electric field to the flow of the spinning solution. During electrospinning, the well-dispersed GONRs were highly oriented along the fiber axis in an electrified thin liquid jet. The addition of GONRs at a low weight fraction significantly improved the mechanical properties of the composite nanofiber yarns. In addition, the carbonization of the matrix polymer enhanced not only the mechanical but also the electrical properties of the composites. The electrical conductivity of the carbonized composite yarns containing 0.5 wt% GONR showed the maximum value of 165 S cm(-1). It is larger than the maximum value of the reported electrospun carbon composite yarns. Interestingly, it is higher than the conductivities of both the PAN-based pristine CNF yarns (77 S cm(-1)) and the monolayer GNRs (54 S cm(-1)). These results and Raman spectroscopy supported the hypothesis that the oriented GONRs contained in the PAN nanofibers effectively functioned as not only the 1-D nanofiller but also the nanoplatelet promoter of stabilization and template agent for the carbonization.