An effective way to optimize the electrode performance of metal oxide was developed by employing exfoliated 2D RuO2 nanosheet as a conducting additive. The exfoliated RuO2 nanosheet was easily incorporated into the Li-MnO2 nanocomposite via a simple mixing of exfoliated RuO2 and MnO2 nanosheets, followed by the restacking with Li+ ions. The incorporation of RuO2 nanosheet was found to be quite effective in increasing the surface area of the restacked Li-MnO2 nanocomposite. The obtained heterolayered Li-MnO2-RuO2 nanocomposites delivered much greater specific capacitances than do the pristine Li-MnO2 and Li-RuO2 nanocomposites. Considering the fact that the RuO2 nanosheet has higher electrode activity than the MnO2 nanosheet, the greater specific capacitance of Li-MnO2-RuO2 nanocomposite than that of Li-RuO2 strongly suggests that the incorporation of a small amount of RuO2 nanosheet into the restacked Li-MnO2 nanocomposite induces a synergistic improvement in its electrode activity. Of prime importance is that the Li-MnO2-RuO2 nanocomposites showed somewhat better electrode performances than the reduced graphene oxide (rG-O)-incorporated Li-MnO2-rG-O homologues, attributable to more efficient charge transport and pore structure upon RuO2 incorporation. The hydrophilic RuO2 nanosheet is more effective in making a stronger chemical interaction with hydrophilic MnO2 and also in depressing the self-aggregation of nanosheets compared to hydrophobic rG-O nanosheet. The present study clearly demonstrates that the RuO2 nanosheet can be used as a better additive for improving the electrode performance of metal oxides compared with widely used rG-O.