Abstract: Application of the nano-NiO in the electrochemical capacitors was studied. The nano- Ni（OH）₂ powder was obtained by mixing aqueous solutions of Ni（NO₃）₂ and KOH in the ammonia water. By heating the nano-Ni（OH）₂ in 300℃,the nano-NiO was obtained （diameter≈30nm）. Using the nano-NiO powders as active material of EC, the electrode can provide a specific capaci- tance of 90～110F/g. The relationship between the specific capacitance and the concentration of the KOH solution and the range of the work potential was studied. The mechanism how the NiO stores charges was discussed.