In this work, NiO nanoparticles with diameter of similar to 4.5 nm for application as electrode material in super capacitor were directly synthesized by an one-pot solvothermal strategy using N,N-dimethylformamide (DMF) as solvent and hexadecyl trimethyl ammonium bromide (CTAB) as additive. The experiment results indicated that CTAB is the key for the phase formation of NiO. Ni(OH)(2) phase was formed in the absence of CTAB, while NiO phase was produced in the presence of CTAB as an additive. As compared with the NiO prepared by calcination on the layer-structured Ni(OH)(2) intermediate produced in the absence of CTAB, the NiO nanoparticles prepared by this strategy had smaller particle size. Due to large specific surface area, small size and residual Ni(OH)(2), these NiO nanoparticles presented high electrochemical performance. They had high specific capacitance of 1128 F g(-1) at low current density of 3.1 A g(-1) and 625.0 F g(-1) at high current density of 62.5 A g(-1). (C) 2019 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.