Abstract: MnO₂·nH₂O as electrode material for supercapacitor was prepared by chemical copreci-pitation. The material was characterized by using X-ray diffraction （XRD）, scanning electron micro-scopy （SEM）, surface area analysis （BET） and Fourier transform infrared spectroscopy （FT-IR）. Theresults show that the material has amorphous structure with particle diameter range from 40 nm to 50 nm,and the BET specific surface area reaches 160.5 m²/g. Electrochemical characterizations were carried out by using cyclic voltammetry（CV） and constant current charge/discharge with a three-electrode system. The results show that within the potential window range from 0 to 0.8V （vs. SCE） amorphous α-MnO₂·nH²O exhibits excellent capacitance and high power characteristics in 0.5 mol/L K₂SO₄ aqueous electrolyte. A maximum specific capacitance of 140 F/g is obtained at the sweep rate of 4 mV/s. Effect of different sweep rates on the specific capacitance of α-MnO₂·nH₂O was also studied.