To investigate the role of Fe ions for oxygen evolution reaction, a series of BaZrxFe1-xO3-delta (0 <= x <= 0.2) perovskite oxides were synthesized and systematically evaluated as electrocatalysts. The OER activity of cubic BaZrxFe1-xO3-delta (0.05 <= x <= 0.2) is higher than that of the parent BaFeO3-delta with a monoclinic structure and close to that of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF), indicating cubic perovskite structure is favorable to the OER, and Fe ions are active for the reaction. Moreover, for cubic BaZr0.15Fe0.85O3-delta samples, the OER performance is closely related to the ratio of Fe4+ to Fe3+, which was tuned by treating BaZr(0.15)Fe(0.8)5O(3-delta) powders at 500 degrees C for 5 h at different atmospheres, such as O-2, air, Ar and 5% H-2/Ar mixture. (C) 2017 Elsevier Ltd. All rights reserved.