The development of electrocatalysts has emerged as an important aspect of rechargeable lithium-oxygen (Li-O2) batteries due to the fact that they facilitate the formation and decomposition of discharge products, leading to a higher capacity and cyclability. Herein, we demonstrate that ruthenium oxide (RuO2) inverse opal (IO), which possesses a three-dimensionally ordered porous network, has been developed and applied to the Li-O2 battery as a cathode. The RuO2 IO cathode contributes to the reduction of charge overpotential by up to ∼120 mV in lithium nitrate/dimethyl sulfoxide (LiNO3/DMSO), which corresponds to an ∼670 mV decrease as compared with that of a carbon cathode, Ketjen black (KB). Differential electrochemical mass spectrometer (DEMS) monitoring and magic angle spinning nuclear magnetic resonance (MAS NMR) measurement reveal the origin of the extremely low charge overpotential obtained from the RuO2 IO cathode by confirming the formation of lithium hydroxide (LiOH) as the main discharge product. The incorporation of RuO2 also remarkably reduces the formation of byproducts such as lithium carbonate (Li2CO3) by substantially lowering the charge overpotential. A mechanistic explanation of the device operation is provided in this study as well.