A sulfide solid electrolyte includes: an ionic conductor including a PS43− unit, a P2S64− unit, and a P2S74− unit; and a lithium compound containing a halogen element, wherein a molar ratio of the P2S64− unit to the PS43− unit is about 1:1 to about 5:1, and a molar amount of the P2S74− unit with respect to the total molar amount of the PS43− unit, the P2S64− unit, and the P2S74− unit is greater than 0 to about 60%.