Most non-aqueous lithium-air batteries reported in the literature are limited to operating with pure oxygen. To practically operate the battery in ambient air, understanding how the battery’s performance varies with humidity of moist air is essential. Here we study the effects of moist air on the cycling performance through operating a non-aqueous lithium-air battery with a stable anode and a nano-structured RuO2/NiO cathode at various relative humidities. Results show that in the dry air, the discharge and charge terminal voltages are around 2.51 and 4.12V, respectively, but change to 2.79 and 3.87V when the relative humidity reaches 84%. The energy efficiencies corresponding to the dry air and the relative humidity of 84% are 66.2% and 73.8%, respectively. The improved performance is found to be mainly due to the increased fraction of LiOH among the discharge products at high relative humidities. The discharge voltage for the formation of LiOH is higher than that for the formation of Li2O2, while the charge voltage for the decomposition of LiOH is lower than that for the decomposition of Li2O2. The results suggest that to enable a non-aqueous lithium-air battery to operate in moist air, in addition to protecting the lithium anode from water, designing a cathode with electrocatalytic activities for the decomposition of both Li2O2 and LiOH is required.