A mixed aqueous/aprotic Na-air cell that works at room temperature has been fabricated and its discharge properties have been examined experimentally as a primary cell. A dense Na3Zr2Si2PO12 ceramic with an ionic conductivity of 1.3 x 10(-3) S.cm(-1) at 25 degrees C and a porous electrode containing Mn3O4 catalyzed carbon are used as a solid electrolyte separator and an air electrode, respectively. This cell gives a maximum output power density of 21 mW.cm(-2) at 25 degrees C, which is one of the best results among alkali metal-air cells reported to date. Electrochemical impedance spectroscopy reveals that a reduction in ohmic resistivity of the ceramic separator is now crucial for a further increase in power density. (C) 2015 The Electrochemical Society. All rights reserved.