Three-dimensional porous NiO/Ni(OH)(2) composites consisting of NiO nanoparticles and amorphous Ni(OH)(2) nanosheets were prepared successfully for supercapacitors. NiO nanoparticles were dispersed uniformly among Ni(OH)(2) nanosheets. The capacitance of the composites reached 1375.45 F g(-1) at 0.5A g(-1), which was much higher than that of pure NiO and Ni(OH)(2). After 1000 cycles, 95.5% of the capacitance of composites was retained. Moreover, an NiO/Ni(OH)(2)-2//AC device was fabricated and exhibited a prominent energy density of 28.5 Wh kg(-1) at a power density of 450 W kg(-1) and even 13.8 Wh kg(-1) at 2258.2 W kg(-1). A light-emitting diode can easily be lit using the device, demonstrating its application. The enhanced capacitance performance of the NiO/Ni(OH)(2) hierarchical structure was ascribed to its tremendous surface area and amorphous characteristics.