Oxygen evolution reaction (OER) is a key process in various advanced technologies for renewable energy conversion, such as water splitting and metal-air batteries. However, as a four-electron coupled reaction, the OER is kinetically sluggish and limited by its high overpotential and low efficiency. The design of novel nanostructured electrocatalysts is highly desirable to promote OER kinetics. Herein, a bio-inspired nanoleaf electrocatalyst has been successfully achieved for the first time by in situ growing ultrathin NiCo layered double hydroxide (LDH) nanosheets on CuO nanowires. Attributed to the mechanical support of CuO nanowire veins, the NiCo LDH lamina presents a large lateral size (more than 10 mu m) and unique hierarchical structure that consisted of ultrathin nanosheets with numerous exposed edges. The CuO veins distributed across the LDH lamina can serve as the fast path for charge transfer and significantly promote the LDH conductivity. Compared to the conventional NiCo LDH nanosheets, the novel nanoleaves with enlarged electrochemical surface area, edge-rich active sites, and improved conductivity exhibit greatly enhanced OER performances with an impressive 9.3 fold enhanced activity, much lower overpotential of 262 mV at 10 mA cm(-2), as well as good stability and flexibility. The biomimetic nanoleaf structures and the corresponding design strategy can be broadly applied to other functional 2D materials for advanced applications.