Disclosed is a composition (an anti-hyperglycemic agent) which has an activity to decrease the blood glucose level in a person who has a high blood glucose level and therefore can be used for decreasing the blood glucose level in the person. Also disclosed is a composition (a prophylactic or therapeutic composition for diseases associated with high blood glucose levels, an anti-diabetic agent) which can be used for the prevention or treatment of diseases associated with high blood glucose levels, specifically diabetes and diabetes complications relying on the above-mentioned activity. The composition is characterized by comprising a peptide having an amino acid sequence: Leu-Ser-Glu-Leu as an active ingredient.
