We synthesized anionic waterborne polyurethane (aWPU) from IPDI (di-isocianate), PTMG (diol), DMPA (anionic ionomer), TEA (neutralizer), and BD (chain extender). Cationic WPU (cWPU) was also prepared using MDEA (cationic ionomer) and HCl (neutralizer) instead of DMPA and TEA. Since the graphene oxide (GO) is anionic due to the –COOH group, GO and aWPU are not compatible because of the repulsive force between identical ionic charges. Thus, we fabricated cationic surfactant treated GO/aWPU to increase the compatibility. cWPU/GO, where attractive forces act between anionic GO and cationic WPU, was also prepared. The thermal stability, glass transition temperature, and mechanical properties of the nanocomposites were investigated. The thermal stability of the WPU was enhanced with the incorporation of GO nanosheets. The glass transition temperature of the hard segment of WPU was increased by the incorporation of GO. These results are attributed the fine dispersion of GO in WPU and strong interfacial interactions between GO and WPU. Enhanced dispersion and interfacial interaction lead to better mechanical properties. Tensile strength, initial modulus, and elongation-at-break of WPU/GO nanocomposites were increased with the incorporation of GO nanosheets. By a simple method (anion-cation matching) we could prepare WPU/GO nanocomposites with enhanced stiffness and toughness.