In this research work, we have prepared the pure and Mg-doped MnO2 nanostructures as electrode material via the facile hydrothermal method. The structure, crystallite size, and morphology of the synthesized samples were characterized using powder X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The X-ray diffraction pattern indicated the tetragonal phase formation of MnO2 nanostructures without any impurity peak. The average crystallite size was calculated by means of the Scherrer formula. SEM study also revealed the formation of nanofibres and nanorods, which enhanced the charge storage capability. Electrochemical performances for pure as well as doped MnO2 samples are also examined in the three-electrode set-up by utilizing the techniques like Electrochemical Impedance Spectroscopy, Cyclic Voltammetry, Galvanostatic Charge Discharge. The specific capacitance of 240.5F/g at 0.5 mA is obtained in the KNO3 electrolyte for the synthesized pure material. Mg doping enhanced the electrochemical performance by nearly 1.5 times and obtained the capacitance of 360F/g at 0.5 mA which can be attributed to the increased lattice defects and oxygen vacancies due to the incorporation of Mg2+ ions in the matrix of MnO2. Therefore, as a consequence of electrochemical performance, Mg-doped MnO2 nanostructures are ideally suitable for supercapacitor applications.