Provided is a method for producing an ion-conductive substance from starting materials of: one or more types of compound selected from phosphorus sulfide, germanium sulfide, silicon sulfide, and boron sulfide; a sulfide of a metal element belonging to Group I or Group II of the periodic table; and a halogen compound represented by MwXx, and including a step for contact thereof within a solvent. (In the formula, M is Li, B, Na, K, Rb, Cs, Ca, Mg, Sr, Ba, Al, Si, P, S, Ge, As, Se, Sn, Sb, Te, Pb or Bi; w is 1 or 2; X is F, Cl, Br, or I; and x is any integer selected from 1 to 10 inclusive);.