Development of acid-stable electrocatalysts with low overpotential for oxygen evolution reaction (OER) is a major challenge to produce hydrogen directly from water. We report in this paper a pyrochlore yttrium ruthenate (Y2Ru2O7-delta) electrocatalyst that has significantly enhanced performance toward OER in acid media over the best-known catalysts, with an onset overpotential of 190 mV and high stability in 0.1 M perchloric acid solution. X-ray absorption near-edge structure (XANES) indicates Y2Ru2O7-delta electrocatalyst had a low valence state that favors the high OER activity. Density functional theory (DFT) calculation shows this pyrochlore has lower band center energy for the overlap between Ru 4d and O 2p orbitals and is therefore more stable Ru-O bond than RuO2, highlighting the effect of yttrium on the enhancement in stability. The Y2Ru2O7-delta pyrochlore is also free of expensive iridium metal and thus is a cost-effective candidate for practical applications.