To provide a simple method of efficiently producing a sulfide salt such as sodium sulfide and sodium disulfide in an alkali solution in an alkali recovery process in the production of pulp.

A sulfide salt such as sodium sulfide and sodium disulfide is efficiently produced by adding and mixing sulfur into an alkali solution comprising sodium sulfide in an amount of at least 10 mass%. A method of producing a sulfide salt according to the method wherein a green liquid is employed as the alkali solution comprising sodium sulfide in an amount of at least 10 mass%, is preferable. Further, a method of producing a sulfide salt according to the method wherein the amount of sulfur added is not greater than 0.5 mass% relative to the amount of sodium sulfide contained in the solution, is preferable.