Moisture in air is a major obstacle for realizing practical lithium-air batteries. Here, we integrate a hydrophobic ionic liquid (IL)-based electrolyte and a cathode composed of electrolytic manganese dioxide and ruthenium oxide supported on Super P (carbon black) to construct a promising system for Li-O-2 battery that can be sustained in humid atmosphere (RH: 51%). A high discharge potential of 2.94 V and low charge potential of 3.34 V for 218 cycles are achieved. The outstanding performance is attributed to the synergistic effect of the unique hydrophobic IL-based electrolyte and the composite cathode. This is the first time that such excellent performance is achieved in humid O-2 atmosphere and these results are believed to facilitate the realization of practical lithium-air batteries.