A simple hydrothermal synthesis method is adopted to prepare nickel oxide/carbon nanotube (NiO/CNT) composites. X-ray diffraction, differential scanning calorimetry/thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, and N-2-adsorption/desorption techniques are employed for morphology and structure characterizations. The different morphologies of NiO are obtained, which change from a two-dimensional flake to a zero-dimensional mesoporous sphere, dispersing on the surface of CNTs by changing the sodium dodecyl sulfate's fraction in the reacting system. The electrochemical performance of NiO/CNT composites is largely affected by the morphology and distribution of the NiO phase. The zero-dimensional mesoporous sphere NiO shows the largest specific capacitance of 1329 F g(-1) as well as a good cycle life during 1000 cycles in a 1 M KOH electrolyte at a very high current density of 84 A g(-1) by chronopotentiometry measurement. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3425624] All rights reserved.