The research investigated the thermal and mechanical properties of graphene/epoxy nanocomposites. Pristine graphene and functionalized graphene were used as nano-reinforcement in the nanocomposites. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS). Results indicated that the pristine graphene contains OH functional group. On the other hand, there are two kinds of functionalized graphene, one contains carboxyl (COOH) group and the other contains COOH and amine (NH2) groups. It was found that the graphene containing NH2 and COOH functional groups exhibits superior reinforcement than the graphene with only COOH functional group. The improvement in mechanical and thermal properties of nanocomposites may be attributed to the enhanced interfacial thermal conductance and interfacial interaction caused by the functional groups. In addition, Young's modulus and thermal conductivity of the nanocomposites increase when the graphene loading increases. However, the fracture toughness and tensile strength of the nanocomposites attain peak values when the functionalized graphene loading is 0.1 wt%.