The nanomechanical properties of polymers that contained poly(styrene-co-methyl methacrylate) (STY-co-MMA) composites with reduced oxide graphene 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 co-polymers 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 increased due to increased mechanical interlocking between the RGO nano-fillers and the (STY-co-MMA) 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 microwave irradiation (MWI) method.