Efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts are closely associated with many important energy conversion technologies. Herein, we first report an oxygen-evolving cobalt-citrate metal-organic framework (MOF, UTSA-16) for highly efficient electrocatalytic water oxidation. Benefiting from synergistic cooperation of intrinsic open porous structure, in situ formed high valent cobalt species, and existing Co4O4 cubane, the UTSA-16 exhibits excellent activity toward OER catalysis in alkaline medium. The UTSA-16 needs only 408 mV to offer a current density of 10 mA cm-2 for OER catalysis, which is superior to that of most MOF-based electrocatalysts and the standard Co3O4 counterpart. The present finding provides a better understanding of electroactive MOFs for water oxidation.