Mn3O4/multiwalled carbon nanotube (MWCNT) nanocomposites were synthesized via a facile ultrasonic method, using manganese chloride as a precursor at room temperature for supercapacitor applications. The nanocomposites were characterized by powder x-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM), respectively. TEM images revealed that the Mn3O4 nanoparticles were highly dispersed on the surface of the MWCNT. Cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS) were performed for the Mn3O4/MWCNT nanocomposites using 1 M Na2SO4 aqueous solutions as the electrolyte in order to find the suitability of the material for supercapacitor applications. The electrochemical results exhibit improved performance for the Mn3O4/MWCNT composite electrode compared to pristine Mn3O4 nanoparticles owing to its structural superiority. The specific capacitance (Cs) of Mn3O4/MWCNT nanocomposites and pristine Mn3O4 was about 473 F g−1 and 259 F g−1, respectively, at a current density of 1 A g−1. The Mn3O4/MWCNT composite sustains a very strong cyclic performance after 5000 cycles. The capacitance retention of the composite electrode shows highly stable performance confirming its suitability as lasting electrode material for supercapacitor applications.