A sulfide solid electrolyte includes 60 mass % or more of a sulfide-based glass phase. The sulfide solid electrolyte includes Li, P, and S as constituent elements, a composition of the sulfide solid electrolyte satisfies Li/P≥2.5, and the sulfide solid electrolyte has a lithium ion conductivity of more than 1 mS/cm at 25° C. when formed into a powder compact at 380 MPa.