Conventional amino acid compositions are primarily intended to improve athleticperformance or to promote fat-burning. Provided is an anti-fatigue agent whichcan prevent both of muscle fatigue and nerve strain concurrently. An anti-fatigueagent which comprises an amino acid composition composed of specific amino acidsin specified amounts can prevent both of muscle fatigue and nerve strain concurrently. As for the types and the ratio of the amounts of the amino acids contained in theamino acid composition, the amino acid composition preferably contains 30 to200 parts by weight of proline, 60 to 140 parts by weight of glycine, 50 to 260 partsby weight of alanine, 50 to 130 parts by weight of lysine, 30 to 75 parts by weightof tryptophan and 20 to 40 parts by weight of histidine, more preferably furthercomprises 3 to 75 parts by weight of tyrosine and 15 to 45 parts by weight of arginine,still more preferably further contains 30 to 55 parts by weight of valine, 35 to60 parts by weight of leucine and 25 to 60 parts by weight of isoleucine.
