This study describes the assembly of a rechargeable seawater battery using hard carbon as the anode, seawater as the cathode, and a fast Na ion-conducting ceramic as the solid electrolyte. Two different Na ion-conducting ceramics, beta ''-Al2O3 and Na3Zr2Si2PO12 (NASICON), are used as the solid electrolytes in this study. The discharge capacity of the seawater battery with the NASICON solid electrolyte is 120 mAh g(-1) after the first cycle and over 91% coulombic efficiency after twenty cycles. However, under the same experimental conditions, the discharge capacity of the seawater battery with a beta ''-Al2O3 electrolyte significantly drops to 10 mAh g(-1) after one cycle. It is observed that the stability of NASICON in seawater is superior to that of beta ''-Al2O3 and impedance results of NASICON are not changed significantly compared to that of beta ''- Al2O3 after cycling tests. The stability of Na ion- conducting ceramics in seawater and their effects on the electrochemical performance of seawater batteries are presented and discussed. (C) 2016 Elsevier Ltd. All rights reserved.