A SOLID OXIDIZED GLUTATHIONE SALT IS PRODUCED BY HEATING AN OXIDIZED GLUTATHIONE AT 30°C OR HIGHER WHILE THE OXIDIZED GLUTATHIONE IS BROUGHT INTO CONTACT WITH AN AQUEOUS MEDIUM IN THE PRESENCE OF A SUBSTANCE FOR PROVIDING A CATION, TO PRODUCE THE SALT OF THE OXIDIZED GLUTATHIONE AND THE CATION AS A SOLID, WHEREIN THE AQUEOUS MEDIUM IS COMPOSED OF WATER AND/OR A WATER-SOLUBLE MEDIUM, AND THE CATION IS AT LEAST ONE SELECTED FROM AN AMMONIUM CATION, A CALCIUM CATION AND A MAGNESIUM CATION.