It is intended to provide an anti-fatigue agent capable of preventing both muscle fatigue and nerve fatigue simultaneously. According to the invention, both muscle fatigue and nerve fatigue can be simultaneously prevented with the anti-fatigue agent containing an amino acid composition comprising specific types and specific amounts of amino acids. With regard to preferred amino acid types and amount ratios, it is an amino acid composition containing 30 to 200 parts by weight of proline, 60 to 140 parts by weight of glycine, 25 to 260 parts by weight of alanine, 40 to 130 parts by weight of lysine, 20 to 75 parts by weight of tryptophan, and 15 to 40 parts by weight of histidine. Further, it preferably contains 35 to 65 parts by weight of threonine, 15 to 65 parts by weight of tyrosine, and 25 to 45 parts by weight of arginine, and further, it preferably contains 30 to 55 parts by weight of valine, 35 to 60 parts by weight of leucine, and 25 to 45 parts by weight of isoleucine.
