Developing highly efficient oxygen evolution reaction (OER) electrocatalysts is critical to the cost-effective generation of clean fuels. Transition-metal selenides have been proposed to be OER catalyst alternatives to noble metal based catalysts, but generally exhibit limited electrocatalytic activity. We here report hierarchical Fe-doped NiSe ((Ni,Fe)Se) ultrathin nanosheets as an efficient electrocatalyst for OER in alkaline electrolytes. The preparation involves a solvothermal synthesis and a topotactic conversion process. The prepared hierarchical (Ni,Fe)Se ultrathin nanosheets show abundant and accessible catalytically active sites, facile charge transfer and a high specific surface area. Relative to the NiSe nanosheets, the as-prepared (Ni,Fe)Se ultrathin nanosheets show a higher current density and a lower Tafel slope towards the OER. Remarkably, hierarchical (Ni,Fe)Se ultrathin nanosheets supported on Ni foam exhibit an electrocatalytic OER with a current density of 10 mA cm at a low overpotential of 225 mV and a small Tafel slope of about 41 mV dec. This study establishes (Ni,Fe)Se ultrathin nanosheets as an efficient electrocatalyst for the OER that can be used in the fields of metal-air batteries and water splitting for hydrogen production.