Water electrolysis (WE) involves both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Because the kinetics of the OER are much slower than those of the HER, the overall efficiency of electrolysis is decreased. Furthermore, since the OER occurs in extremely harsh environments, stability of materials needs to be considered for WE application. To overcome this challenge, researchers have conducted many studies to investigate OER catalysts. In the current study, to achieve a balance between activity and stability, three-dimensional mesoporous IrO2/RuO2 (MS-IrO2/RuO2) was prepared via nano-replication and the Adams method sequentially, and for comparison, Ir-Ru binary oxides (IrO2/RuO2) with a high specific surface area were synthesized using commercial RuO2 via the Adams method. Thereafter, the effects of the structural and electrochemical characteristics of the catalysts on the OER activity were analyzed. MS-IrO2/RuO2 with an Ir/Ru molar ratio of 1:10 was shown to have a lower overpotential (300 mV at 10 mA cm(geo)(-2)) than conventional IrO2/RuO2 (340 mV). After the accelerated stability test for over 2 h using the chronopotentiometry technique, the increase in overpotential was as low as 22 mV for MS-IrO2/RuO2, lower than that of IrO2/RuO2 (44 mV). The results of this work are anticipated to prove useful to aid researchers in better understanding viable approaches for improving OER performance.