In this paper, we report the growth of ultrathin Ni(OH)2 nanosheets on nickel foam at room temperature via a cost-effective and simple process, oxidizing fresh nickel foam in a wet environment followed by a morphology transformation in a mixed alkaline and oxidative solution without the need for any additional nickel sources, templates, or surfactants. When tested as electrode for a supercapacitor, the Ni(OH)2 nanosheets grown on nickel foam displayed excellent performance, demonstrating specific capacitance of 2384.3Fg−1 at a charge and discharge current density of 1Ag−1 and 1288.1Fg−1 at 5Ag−1 with a good cycling ability (~75% of the initial specific capacitance remained after 3000 cycles). The excellent electrochemical performance is attributed to its unique nanostructures, which may facilitate rapid ion transport near electrode surfaces, while allowing facile redox reactions associated with charge storage by the nanosheets. The demonstrated high specific capacity and the remarkable rate performance of the Ni(OH)2 nanosheets, together with the flexibility of the nickel foam substrate, make the three-dimensional nanostructured electrodes ideally suited for low-cost, high-performance supercapacitor applications.