Conventional amino acid compositions are primarily intended to improve athletic performance or to promote fat-burning. Provided is an anti-fatigue agent which can prevent both of muscle fatigue and nerve strain concurrently. An anti-fatigue agent which comprises an amino acid composition composed of specific amino acids in 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 the amino acid composition, the amino acid composition preferably contains 30 to 200 parts by weight of proline, 60 to 140 parts by weight of glycine, 50 to 260 parts by weight of alanine, 50 to 130 parts by weight of lysine, 30 to 75 parts by weight of tryptophan and 20 to 40 parts by weight of histidine, more preferably further comprises 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 to 60 parts by weight of leucine and 25 to 60 parts by weight of isoleucine.
