The present invention relates to a method of improving the preservation stability of glutathione, which is characterized by allowing glutathione to co-exist with an arginine-acidic amino acid salt. In addition, the present invention relates to a production method of a glutathione preparation, which is characterized by mixing glutathione and an arginine-acidic amino acid salt. By the production method, a glutathione preparation that resists quality deterioration can be provided. Moreover, the present invention relates to a preservation method of glutathione, which is characterized by allowing glutathione to co-exist with an arginine-acidic amino acid salt. By the preservation method, quality deterioration of glutathione during preservation can be suppressed.