Oxygen evolution reaction (OER), as the critical step in splitting water, is a thermodynamically "up-hill" process and requires highly efficient catalysts to run. Arrhenius' law suggests that the higher temperature, the faster the reaction rate, so that a larger OER current density can be achieved at a lower eta. Herein, we report an abnormal temperature effect on the performance of Co-based catalysts, e.g., Co3O4, Li2CoSiO4, and Fe-doped Co(OH)(x), in OER in alkaline electrolytes. The OER performance reached a maximum when the temperature increased to 65 degrees C, and the OER performance declined when the temperature became higher. The mechanism was investigated by using Co3O4 as a model sample, and we propose that at an optimal temperature (around 55-65 degrees C) the main rate-determining step changes from OH- adsorption dominant to a mixed mode and both the adsorption and the cleavage of the OH group can be rate-determining, which leads to the fastest kinetics.