Design and fabrication of high performance energy storage devices using different mixed metal oxides decorated on conducting 2D surfaces are being investigated intensively now a days. In the present work, we have explored to synthesize a new mixed metal oxide (RuNi₂O₄) containing Ru and Ni and decorate the nanoparticles of these mixed metal oxides on highly conducting 2D reduced graphene oxide (rGO) surfaces to prepare efficient electrodes for high performance supercapacitors. The microstructure and compositional analyses of the composite structure are carried out by powder X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The XRD data have been analysed by Rietveld refinement. The electrochemical performance of the device has been investigated via galvanostatic charging-discharging (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analyses. It is seen that RuNi₂O₄/rGO composite shows a very high specific capacitance of 792 Fg⁻¹ compared to the values of rGO and pristine RuNi₂O₄ as 235 and 367 Fg⁻¹, respectively. Due to the combined effect of the electric double layer contribution of rGO and the faradaic contribution of RuNi₂O₄, RuNi₂O₄/rGO composite results in this high value of specific capacitance in the composite structure.