The nanomechanical properties of polymers that contained (styrene methyl methacrylate) copolymer (PS-PMMA) composites with reduced graphene oxide sheets (RGO) prepared by (i) in situ bulk polymerization and (ii) a microwave irradiation (MWI) method were compared. The nanomechanical properties such as the hardness and elastic modulus of these copolymers were analyzed using Berkovich nanoindentation. The results indicate that the composite obtained using the MWI method exhibited a better morphology and increased dispersion with enhanced thermal stability. As a result, the mechanical properties also improved due to increased mechanical interlocking between the graphene oxide (GO) nanofillers and the PS-PMMA matrix, which improved the mechanical strength. An average increase of 136% in hardness and 76% in elastic modulus were achieved through the addition of only 2.0 wt % of RGO composite obtained via the MWI method.