Developing highly efficient and stable electrocatalysts in acidic media is essential for proton exchange membrane water electrolyzers (PEMWEs). Especially for oxygen evolution reaction (OER), high overpotential is needed to overcome the high thermodynamic energy barrier of water splitting. Herein, we report a high‐efficiency self‐supported ternary alloy OER catalyst with high activity and good durability in acidic electrolytes by a simple electrodeposition method. The as‐prepared electrocatalyst consists of Ru, Au, and Mn alloy which is deposited on the carbon fiber paper (denoted as RuAuMn‐CFP). The RuAuMn‐CFP exhibits superior activity and only requires an overpotential of 131 mV at 10 mA cm−2 and outstanding stability of 30 h (10 mA cm−2) in acidic media, which outperforms the commercial Ru/C and Ir/C catalysts. Besides, at an overpotential of 140 mV, the RuAuMn‐CFP catalyst exhibited a remarkable mass activity of 29.63 mA/mg for OER. It is 7.9 times and 23.8 times higher than the commercial Ru/C and Ir/C catalysts (3.73 mA/mg, 1.24 mA/mg, respectively).