Fluoride-ion batteries using solid-state electrolytes exhibit the high theoretical energy density and one of the candidates for next-generation rechargeable batteries [1]. For fluoride-ion batteries, the ion carrier is monovalent fluoride ion, which can realize the multi-electron reactions of counter cations in active materials of fluoride compounds. However, it is far from practical use because there is no solid electrolyte which has high ionic conductivity and a wide electrochemical potential window like lithium-ion conductors. The previously reported fluoride-ion conductors such as PbSnF4 [2] and La0.9Ba0.1F2.9 [3] contain single carrier ion, fluoride ions. To our best knowledge, there is few report on the solid electrolyte materials containing multiple-anion compounds [4].In the field of material sciences, mixed-anion compounds have recently attracted attention, and unique structures with multiple anions have been reported [5]. Compared with existing materials such as oxides and fluorides, mixed-anion compounds have the possibilities to exhibit innovative functions due to their specific crystal and coordination structure. Therefore, using multiple-anion compounds could realize much higher physical properties than ever before.In this study, we synthesized La-Sr-F-S compounds containing fluoride and sulfides ions as anions by solid-state reaction under vacuum. The crystal structure of the synthesized compound was characterized by X-ray diffraction. In order to measure the conductivity and the fluoride-ion transport number of the synthesized compounds, electrochemical impedance spectroscopy and the DC conductivity measurement were performed, respectively. Moreover, cyclic voltammetry was performed to evaluate electrochemical potential window. In the synthesis, F-- deficient and F--excess type of La-Sr-F-S compounds were successfully synthesized by controlling the weight ratio of starting materials. We discuss the mechanism to realize fast fluoride ion conduction comparing them.Reference:[1] M.A. Reddy and M. Fichitner, J. Mater. Chem, 21, 17059–17062 (2011).[2] N. I. Sorokin, P. P. Fedorov, O. K. Nikol’skaya, O. A. Nikeeva, E. G. Rakov, and E. I. Ardashinikova, Inorg. Chem., 37, 1178-1182 (2017)[3] C. Rongeat, M. A. Reddy, R. Witter, and M. Fichtner, ACS Appl. Mater. Interfaces, 6(3), 2103-2110 (2014).[4] S. Mater, J. Reau, L. Rabardel, G. Demazeau, and P. Hagenmuller, Solid State Ionics, 11, 77-81(1983).[5] H. Kageyama, K. Hayashi, K. Maeda, J.P. Attfield, Z. Hiroi, J.M. Rondinelli, and K.R. Poeppelmeier, Nature Comm., 9 772(2018)