In this work, we report an atomic layer deposition (ALD) method for the fabrication of NiO/CNT hybrid structures in order to improve electronic conductivity, enhance cycling stability and increase rate capability of NiO used as supercapacitor electrodes. A uniform NiO coating can be well deposited on carbon nanotubes (CNTs) through simultaneously employing O3 and H2O as oxidizing agents in a single ALD cycle of NiO for the first time, with a high growth rate of nearly 0.3 Å per cycle. The electrochemical properties of the as-prepared NiO/CNT were then investigated. The results show that the electrochemical capacitive properties are strongly associated with the thickness of the NiO coating. The NiO/CNT composite materials with 200 cycles of NiO deposition exhibit the best electrochemical properties, involving high specific capacitance (622 F g(-1) at 2 A g(-1), 2013 F g(-1) for NiO), excellent rate capability (74% retained at 50 A g(-1)) and outstanding cycling stability. The impressive results presented here suggest a great potential for the fabrication of composite electrode materials by atomic layer deposition applied in high energy density storage systems.