Transition metal chalcogenides received much attention as high performance electrode materials for energy storage devices during this decade. In this article, we demonstrated the sonochemical preparation of cubic RuS2 nanoparticles with average size in the range of 20nm and investigated their supercapacitive properties in detail using cyclic voltammetry, charge-discharge analysis and electrochemical impedance spectroscopy, respectively. The RuS2 electrode delivered a specific capacitance of 85Fg−1 at a constant discharge current density of 0.5mAcm−1 using a three electrode configuration. The RuS2 symmetric supercapacitor device delivered a specific capacitance of 17Fg−1 and excellent cyclic stability of about 96.15% capacitance retention over 5000 cycles. The electrochemical impedance spectroscopy (Nyquist and Bode) analysis together with the frequency dependent capacitance (real and imaginary) studies confirmed the ideal capacitive nature of the RuS2 supercapacitor. The experimental findings ensure the potential application of RuS2 nanoparticles as a novel electrode material for electrochemical energy storage devices.