Herein are disclosed an excellent collagen synthesis-promoting amino acid composition that are characterized by containing specific amino acids at a specific ratio, more specifically, by containing 10-40 parts by weight of L-arginine and/or 10-40 parts by weight of L-glutamine, as well as 5-20 parts by weight of L-valine, 8-30 parts by weight of L-isoleucine and 10-35 parts by weight of L-leucine, an amino acid composition that inhibits skin aging, an amino acid composition that suppresses osteoporosis, an amino acid composition that promotes regeneration of tendon and ligament, and an amino acid composition that heals wounds or thermal burns, that are of the same composition.