Abstract The production of green hydrogen in water electrolyzers is limited by the oxygen evolution reaction (OER). State-of-the-art electrocatalysts are based on Ir. Ru electrocatalysts are a suitable alternative provided their performance is improved. Here we show that low-Ru-content pyrochlores (R 2 MnRuO 7 , R = Y, Tb and Dy) display high activity and durability for the OER in acidic media. Y 2 MnRuO 7 is the most stable catalyst, displaying 1.5 V at 10 mA cm −2 for 40 h, or 5000 cycles up to 1.7 V. Computational and experimental results show that the high performance is owed to Ru sites embedded in RuMnO x surface layers. A water electrolyser with Y 2 MnRuO 7 (with only 0.2 mg Ru cm −2 ) reaches 1 A cm −2 at 1.75 V, remaining stable at 200 mA cm −2 for more than 24 h. These results encourage further investigation on Ru catalysts in which a partial replacement of Ru by inexpensive cations can enhance the OER performance.