Abstract: Mn₃O₄nanoparticles were prepared in alkaline solution and their electrochemical characteristics were investigated. The obtained Mn₃O₄ nanoparticles were characterized by scanning electron microscopy(SEM), X-ray diffraction analysis(XRD), cyclicvoltammetry(CV), galvanostatic charge/discharge(GC/D),and electrochemical impedance spectroscopy(EIS). The Mn₃O₄ nanoparticles can be prepared directly in NaOH and NH₃ solution. MnCO₃ is only obtained in Na₂CO₃ solution,and can be transformed to Mn₃O₄ nanoparticles in the presence of NaOH. The crystalline sizes of the Mn₃O₄ nanoparticles prepared in NaOH,NH₃ and Na₂CO₃solution are 29.5 nm, 20.2 nm and 36.3 nm, respectively. The Mn₃O₄ nanoparticles could be conditioned and inverted to birnessite-type MnO₂. A specific capacitance of 239 F/g is obtained for the conditioned Mn₃O₄ nanoparticles prepared in NH₃ solution at a current rate of 0.25 A/g.Therefore,the Mn₃O₄ nanoparticles obtained in NH₃ solution can be a promising electrode materials for supercapacitors.