Nickel oxide with a high surface area showing high capacitance is reported here. Mesoporous microspheres (MMS) of 250NiO, 300NiO, 350NiO, 400NiO and 500NiO are synthesized by calcining mesoporous α-Ni(OH)2 at 250°C, 300°C, 350°C, 400°C, and 500°C, respectively. The mesoporous α-Ni(OH)2 was prepared by a hydrothermal method. 250NiO has the highest specific surface area of 295m2/g, and a high specific capacitance of 1,140Fg⿿1 at a current density of 10Ag⿿1 from galvanostatic discharge measurements. The cyclic voltammetry, galvanostatic discharge measurement and electrochemical impedance analysis exhibited that the pseudocapacitive behavior is more clarified for NiO prepared at higher calcination temperature. Apparently, the high specific capacitance of 250NiO results from the mesoporous pores and high specific surface area enhancing the transportation of ions during the charging and discharging process to store high energy. The power density and energy density of the 250NiO are 2.5kWkg⿿1 and 59W h kg⿿1 respectively at the current density of 10Ag⿿1.