Disclosed is an agent for use in the treatment or prevention of inflammatory bowel disease. Also disclosed is an agent for inhibiting the production of TNF-α. A therapeutic or prophylactic agent for inflammatory bowel disease comprising at least one amino acid selected from the group consisting of lysine, histidine, phenylalanine, methionine, tryptophan, glutamine, glycine, cysteine, cystine and threonine, the amino acid being administered at a dose of 0.1 to 4000 mg/kg per day; and a TNF-α production inhibitor comprising an amino acid selected from the group consisting of histidine, phenylalanine and tryptophan, the amino acid being administered at a dose of 0.1 to 4000 mg/kg per day.