The invention provides a method of improving the preservation stability of glutathione in a solid composition containing glutathione and arginine. In particular, glutathione and arginine are made to be coexistent with an organic acid such as citric acid, tartaric acid, ascorbic acid, malic acid, malonic acid, succinic acid, fumaric acid, maleic acid and the like. The amount of the organic acid to coexistent with glutathione and arginine is generally 0.1-2 parts by weight relative to 1 part by weight of arginine.
