Graphene can be used as a filler for polymer nanocomposites because of its excellent opto-electronic, mechanical, and thermal properties. Of the various graphene-polymer nanocomposites prepared to date, polycarbonate/graphene nanocomposites are very promising for electrostatic discharge (ESD) and electromagnetic interference (EMI) shielding applications because of their outstanding mechanical, thermal, and electrical properties. To date, conventional melt and solvent mixing methods have been widely used to disperse graphenes in polycarbonate (PC) matrixes. However, graphene has a high specific surface area so irreversibly aggregates or restacks in PC matrixes due to the strong van der Waals forces and π-π stacking interactions between graphene layers. Thus, the homogeneous dispersion of graphene in PC matrixes remains a challenge that must be overcome for commercialization.Here, we report a new method for the highly efficient dispersion of graphene nanosheets (GNS) in PC matrixes in which PC is grafted onto graphene nanosheets (PC-g-MGNS). These PC-g-MGNS nanocomposites are synthesized by grafting hydroxyl-terminated PC onto methylene diphenyl diisocyanate-functionalized graphene nanosheets (MGNS). We demonstrate that the homogeneous dispersion of graphene is achieved with this method, which results in PC-graphene nanocomposites with mechanical and electrical properties that are significantly better than those of conventional solvent-mixed PC-graphene nanocomposites (s-PC/GNS). Furthermore, the electrical conductivity of PC-g-MGNS nanocomposites fully satisfies the ESD/EMI range for MGNS loadings below 1.0 wt %.