In this work, mesoporous NiO with three-dimensional flowerlike morphology were synthesized from precursor α-Ni(OH)2 by a facile template-free modified homogeneous precipitation method, where CO(NH2)2 could be acted as a chelating agent at lower temperatures, and source material of OH− utilizing the hydrolysis reaction at high temperatures. The structures of the NiO materials were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The specific surface area of NiO was 140m2 g−1, which was about 86% of the specific surface of precursor α-Ni(OH)2 (163m2 g−1). The pore diameter of NiO and α-Ni(OH)2 were approximately 3.6nm and 1.7nm, corresponding to mesoporous and microporous, respectively. The NiO material used as an electrode in 6molL−1 KOH electrolyte exhibited a specific capacitance of 289Fg−1 at a current density of 5Ag−1, and could still retain 262Fg−1 at 10Ag−1 and 257Fg−1 at 20Ag−1, respectively. In addition, almost no decrease of the capacitance was observed after 4000th charge-discharge cycles at a current density of 10Ag−1.