MnO₂ nanoparticles were incorporated in reduced graphene oxide (rGO) sheets employing an in-situ, one-step and eco-friendly method. The X-ray diffraction result shows that MnO₂ nanoparticles encapsulation increases the interlayer spacing of rGO. The UV-Vis, FTIR, X-ray photoelectron and Raman spectroscopic studies show that MnO₂ nanoparticles are well intercalated within reduced graphene oxide sheets. The electrochemical studies were executed in 0.5 M aqueous sulphuric acid. The maximum 'specific capacitance' value for MnO₂/reduced graphene oxide nanocomposite was 152.5 F/g at 0.05 V/s. The MnO₂/reduced graphene oxide (MnO₂/rGO) nanocomposite sample displayed an excellent charge retention capacity of 92% after 1000 cycles.