Supercritical carbon dioxide (scCO(2)) has been employed in conjunction with vapor growth carbon fibers (VGCFs) and graphene nanoplatelets (GNPs) to enhance the properties (electrical, thermal, physical) of a poly (methyl methacrylate) (PMMA) matrix. When the VGCF loading was 10 wt.%, the electrical conductivity (9.33 S/m) of the PMMA-VGCF nanocomposite prepared through scCO(2) mixing at 103.4 bar and 40 degrees C was 15.6% greater than that obtained when using traditional mixing in N-methyl-2-pyrollidone (NMP). A synergetic effect existed for the VGCFs and GNPs, with the thermal conductivity of the PMMA-VGCF-GNP nanocomposite [0.492 W/(m K)] being 20.2% greater than that of the individual PMMA-VGCF nanocomposite [0.409 W/(m K)], after applying scCO(2) mixing. The advantages of the proposed scCO(2) technology are twofold: it enhances the dispersion of VGCFs and GNPs in the PMMA matrix and eliminates residual NMP after scCO(2) drying.