Graphene nanoplatelets (GNPs), the most important mass-produced graphene, are fabricated as a mechanical reinforcement for epoxy matrix nanocomposites. Current performance of GNPs as a reinforcing filler is limited by their agglomeration and weak interfacial interaction with certain polymer matrices. Herein, an approach to produce noncovalently functionalized GNPs (F-GNPs) is reported that can be extended to the industrial level of mass production. The one-step functionalization process uses melamine, a low-cost chemical, to improve the interfacial adhesion and dispersion in an epoxy matrix. The mechanical properties of nanocomposites prepared with the F-GNP flakes are much better (94.3% and 35.3% enhancements in Young's modulus and tensile strength, respectively) than those of the unfilled pure epoxy. Experimental data are analyzed using the Halpin-Tsai model. The fabrication process developed in this paper provides a strategy to use GNPs at the industrial level in lightweight and high-strength structural applications.