A two-step approach is proposed to prepare high-performance NiO electrode material. First, the scroll-like alpha-Ni(OH)(2) is prepared by hydrothermal reaction via a self-assembly growth process using guanidine hydrochloride as precipitant. Second, the precursor Ni(OH)(2) is converted to NiO by calcination. The resultants of hierarchical mesoporous NiO ultrathin nanosheets are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) patterns and N-2 adsorption and desorption. The electrochemical properties of the samples are evaluated though cyclic voltammetry (CV), charge-discharge and electrochemical impedance spectroscopy (EIS) in 6.0 M KOH electrolytic solution. The results show that the typical hierarchical mesoporous NiO ultrathin nanosheets exhibits a very large specific capacitance of 1060 F g(-1) at 1 A g(-1), an outstanding cyclic stability with a capacitance retention of 91% after 5000 cycles of charge-discharge and a low resistance. (C) 2014 Elsevier B.V. All rights reserved.