Earth-abundant transition metal-based nanomaterials play a signi?cant role in oxygen evolution reaction (OER). Among them, copper has attracted signi?cant attention due to its excellent electrocatalytic activity, low price, and abundance. Herein, a nanostructured copper oxide (CuO-A) is generated in situ from a cuprous selenide (Cu2Se) precursor under oxygen evolution reaction conditions. The as-prepared CuO-A/copper foam (CF) electrode delivers a current density of 10 mA cm(-2) at an overpotential of 297 mV with good stability for over 50 h in 1 m KOH solution, which is superior to most recently reported copper-based water oxidation catalysts. The high catalytic performance of CuO-A is mainly attributed to the improved surface area offered by the morphology reconstruction during the in situ transformation process. As a result, it paves a way to synthesize effective and stable transition metal oxide catalysts via the in situ conversion of transition metal chalcogenides for energy conversion and storage applications.