CoSe/FeSe nanocomposites were synthesized via colloidal synthesis for the first time. Structural analysis indicates the co-existence of CoSe and FeSe in the nanocomposite and the molar ratio between Co and Fe was tuned during the synthetic process. Although no electronic interaction between Co and Fe was observed in the nanocomposite, the presence of FeSe can significantly affect the electrochemical oxidation process of CoSe. The nanocomposites were further tested for electrochemical oxygen evolution reaction (OER) and the optimal composition was found to be CoFe0.7Se1.7, with low onset potential of 1.511 V vs. RHE and small Tafel slope of 43.90 mV dec(-1). Surprisingly, the CoFe0.7Se1.7 catalyst can out-perform the state-of-art RuO2 at a high current density (100 mAcm(-2)). The synergistic effect between Fe and Co in OER catalysis were observed even without doping the metal ions into the crystal lattice of CoSe and the active sites of CoSe and the co-catalyst FeSe were identified as the higher oxidation states of Co3+ and Fe3+. (c) 2018 Elsevier Ltd. All rights reserved.