Single-crystalline Mn3O4 square-shaped nanostructures have been successfully synthesized by hydrothermal method without using any surfactant. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and High Resolution transmission electron microscopy (HRTEM). To assess the potential properties of nanostructures, galvanostatic charging-discharging and cyclic voltammetry measurements were performed for their use in supercapacitors. The Mn3O4 nanoarchitectures used as supercapacitor electrode in 1mol L-1 KOH electrolyte have a specific capacitance value of 355.5 F g-1 at a low current density of 0.35 A.g-1. The device still retain 85.08% of its initial capacitance afterwards 2000 cycles at a current density of 5 A.g-1. The as-synthesized Mn3O4 nanostructures exhibited a good rate capability and stability for electrochemical properties. These results indicate their potential application as electrode material for high performance supercapacitor in basic medium.