This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400°C, the maximum specific capacitance value was found to be as high as 681Fg−1 (or 183Fcm−3), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.