A mixture obtained by mixing ascorbic acid powder with arginine powder in a weight ratio (ascorbic acid/arginine) of 1/5 to 20, especially 1/5 to 1/4; and a supplement such as a nutrient preparation and a health-care food containing the mixture. Mixing of arginine powder and ascorbic acid powder in the weight ratios eliminates stringent taste specific to arginine and alleviates stringent feeling in the stomach (heartburn, nausea or vomiting) after oral intake thereof. The mixture prevents also peroxidative injuries of cells caused by an administration of a great amount of arginine alone. Further, mixing of arginine powder with ascorbic acid powder prevents browning of the mixture after long-term storage.