Efficient oxygen evolution reaction (OER) catalysts made of earth abundant elements are essential for the cost-effective generation of solar fuels. Surface modification is a novel strategy to enhance the activity of OER catalysts, however, it is commonly done under harsh and energy intensive conditions. Herein, we present a facile approach of solvent treatment to hydroxylate the surface of a layered perovskite, Sr3FeCoO7−δ. The catalytic activity correlates with the degree of surface hydroxylation, which influences the absorption energy of intermediates on the surface. The optimized catalyst exhibits higher activity than the current benchmark perovskite OER catalysts. This work introduces a mild and convenient method for surface modification, which may be applicable for the improvement of other nanoscale electrocatalysts.