Na3PS4 solid electrolytes were synthesized by liquid-phase reactions of Na2S and P2S5 in 1,2-dimethoxyethane or diethyl ether. After stirring of the starting materials, white suspensions were obtained. The suspensions were dried at room temperature and heated at 270 degrees C under vacuum to obtain powders. The crystalline phases of the powders were cubic Na3PS4. The pelletized Na3PS4 prepared using 1,2-dimethoxyethane or diethyl ether showed conductivities of 2.6 x 10(-5) S CM-5 or 1.8 x 10(-5) S CM-1 at 25 degrees C, respectively.