(Problem to be Solved) A solid electrolyte material with favorable ion conductivity is demanded from the viewpoint of the higher output of a battery. The present invention was made in view of the above-described problems, with an object of providing a sulfide solid electrolyte material with favorable Li ion conductivity and providing a lithium battery including the sulfide solid electrolyte material. (Solution) There are provided: a solid electrolyte including a sulfide-based solid electrolyte represented by a composition formula: (Li2S)x(MS2)y(P2S5)z, in which M is at least one selected from the group consisting of Ge, Sb, Si, Sn, B, Al, Ga, In, Zr, V, and Nb, and 0.53≤x≤0.74, 0.13≤y≤0.37, 0.04≤z≤0.15, and x+y+z=1 are satisfied; and a lithium battery including the solid electrolyte.