Graphene nanoplatelets (GNPs) are platelet-liked graphite nanocrystals with multi-graphene layers. In general, a high contact area between polymer and nanofiller maximizes stress transfer from the polymer matrix to nanofillers. Therefore, GNPs can be expected to exhibit better reinforcement than CNTs in polymer composites, because of their ultrahigh aspect ratio (600-10,000) and higher surface constant area. The GNPs planar structure provides a 2D path for phonon transport, and the ultrahigh surface area allows a large surface contact area with polymer resulting in the enhancement of the composite thermal conductivity. In this study, simple and efficient planetary mixing methods were used to enable the GNPs to disperse uniformly throughout the epoxy solution (i.e. 0, 0.1, 0.25, 0.5, 0.75, and 1.0 wt%) and then to prepare GNPs/epoxy nanocomposites. Mechanical properties of the nanocomposite, including ultimate tensile, flexural strength and flexural modulus, were investigated. Finally, the fracture surface of the specimen was investigated using scanning electron microscopy (SEM) to determine the dispersion of the GNPs in the composites.