The　M2+-substituted　Nasicons　were　prepared　by　using　the　Nasicon　(Na3Zr2Si2PO12)　as　a　starting　material　whose　Na+　can　be　reversibly　ion-exchanged　with　a　variety　of　divalent　cations,　e.g.　Mg2+,　Ca2+,　Sr2+,　and　Zn2+　in　the　melt　or　the　solution　of　their　salts.　The　results　from　XRD　analysis　show　that　the　M2+-substituted　Nasicon　have　the　same　structure　as　the　original　Nasicon　with　the　space　group　of　C2/c.　The　measurement　results,　through　using　an　a.c.　impedance　technique,　show　that　among　the　M2+-substituted　Nasicons,　the　Mg2+-substituted　one　has　the　highest　conductivity　(1.48×10-2S/cm　at　400°C)　which　can　be　used　as　a　solid　electrolyte　in　a　Mg/CuCl　solid　state　battery　whose　open-circuit　voltage　is　of　2.07V,　short　circuit　current　of　1mA,　mean　discharge　voltage　of　1.6V,　and　cell　capacity　of　3.4mAH.