Developing cost-effective and high-performance bifunctional electrocatalysts for overall water splitting is of great significance. Herein, we report a facile one-step synthesis of low Ru-doped (0.14 wt%) FeOOH nanosheets on nickel foam (RuFeOOH/NF) as a highly efficient bifunctional electrocatalyst. The experimental results show that the Ru doping modulates the electronic configuration of FeOOH, and the nanosheet morphology exposes more activity sites. As a result, the RuFeOOH/NF catalyst provides excellent electrocatalytic activities, requiring overpotentials of only 245 mV for OER and 184 mV for HER at 100 mA cm⁻² in 1 M KOH, respectively. In addition, a alkaline electrolyzer assembled with RuFeOOH/NF electrodes as anode and cathode not only achieves a voltage of 1.8 V at 100 mA cm−2, but also shows good stability. This work provides a promising strategy for designing high-performance bifunctional electrocatalysts for overall water splitting.