Oxygen evolution reaction (OER) is a principal process in electrochemical energy conversion. Unfortunately, the sluggish reaction kinetics of OER hinders large-scale applications of those electrochemical energy conversion technologies. In this article, nickel-based metal-organic framework nanosheets attached on carbon nanotube films were successfully synthesized. The self-supporting electrode exhibits a fascinating activity with an overpotential of 221 mV at a current density of 10 mA cm(-2) and long-term stability with 24 h without noticeable changes of current density. In situ Fourier transform infrared testing reveals the formation of the key active intermediates (HO*, O*, and HOO*) during the OER process. A series of material characterization demonstrated that coordinatively unsaturated metal sites on the Ni BDC are the real active sites in OER.