Li0.2375+xLa0.5875-xSrxTiO3-LaPO4fast　ionic　conductor　was　synthesized　by　high　temperature　solid　state　reaction.　A.　C.　impedance　measurements　show　that　the　system　has　higher　conductivity　in　low　doping　content　of　Sr2+,　but　the　conductivity　goes　down　from　5.78×10-5to　3.11×10-7S·cm-1with　increasing　the　content　of　Sr2+.　The　activation　energy　is　about　20　kJ·mol-1in　the　temperature　range　of　25-400°C.　X-ray　powder　diffraction　shows　that　the　doping　Sr2+would　not　affect　the　structure　of　compositions　in　the　system.　The　main　phase　is　Li0.2375+xLa0.5875-xSrxTiO3perovskite　solid　solution,　LaPO4as　a　second　phase　can　also　be　found.　With　increasing　the　content　of　Sr2+(x＞0.05),　another　phase　SrTiO3appears.　IR　measurement　also　indicates　that　the　structure　of　compositions　in　the　system　would　not　be　affected　by　Sr2+doping.　The　decomposition　voltage　of　Li0.2375+xLa0.5875-xSrxTiO3-LaPO4remain　unchanged　(1.5　V).