Developing highly active and sustained oxygen evolution reaction (OER) catalysts for energy-saving electrolytic hydrogen generation is highly attractive. In this work, we report the development of a Cu3Mo2O9 nanosheet array on nickel foam (Cu3Mo2O9/NF) as a highly active OER catalyst. Such Cu3Mo2O9/NF shows high catalytic activity in 1.0 M KOH, passing 50 mA cm-2 at an overpotential of 325 mV. It also shows superior long-term durability more than 24 h with a turnover frequency (TOF) of 0.09 mol O2 s-1 at overpotential of 400 mV.