Electrochemical capacity retention of nearly X-ray amorphous nanostructured manganese oxide (nanoMnO₂) synthesized by mixing directly KMnO₄ with ethylene glycol under ambient conditions for supercapacitor studies is enhanced significantly. Although X-ray diffraction (XRD) pattern of nanoMnO₂ shows poor crystallinity, it is found that by Mn K-edge X-ray absorption near edge structure (XANES) measurement that the nanoMnO₂ obtained is locally arranged in a δ-MnO₂-type layered structure composed of edge-shared network of MnO₆ octahedra. Field emission scanning electron microscopy and XANES measurements show that nanoMnO₂ contains nearly spherical shaped morphology with δ-MnO₂ structure, and 1D nanorods of α-MnO₂ type structure (powder XRD) in the annealed (600 °C) sample. Volumetric nitrogen adsorption−desorption isotherms, inductively coupled plasma analysis, and thermal analysis are carried out to obtain physicochemical properties such as surface area (230 m² g⁻¹), porosity of nanoMnO₂ (secondary mesopores of diameter 14.5 nm), water content, composition, etc., which lead to the promising electrochemical properties as an electrode for supercapacitor. The nanoMnO₂ shows a very high stability even after 1200 cycles with capacity retention of about 250 F g⁻¹.Read less <