Abstract: Provided is a sulfide solid electrolyte that has a novel crystal structure and exhibits an ionic conductivity, the sulfide solid electrolyte containing a lithium atom, a phosphorus atom, a sulfur atom, and at least one kind of halogen atom selected from a chlorine atom and a bromine atom, and having a specific diffraction peak in powdery X-ray diffractometry using CuK? line, and a method for producing a sulfide solid electrolyte, the method including mixing a solvent 1 having a heteroatom and a raw material 1 containing specific atoms to prepare a mixture, preparing a solution that contains a raw material 2 containing a halogen atom and a solvent 2 having a heteroatom, mixing the mixture and the solution to prepare a fluid, and heating the fluid.