PROBLEM TO BE SOLVED: To provide a novel peptide showing better activities on a glucagon like peptide-1 receptor and a glucagon receptor than native oxyntomodulin, and a composition for prevention or treatment of obesity comprising the peptide as an active ingredient.SOLUTION: The invention provides: a peptide having specific amino acids, such as an oxyntomodulin derivative capable of activating a GLP-1 receptor and a glucagon receptor; a polynucleotide encoding the peptide; and a pharmaceutical composition for prevention or treatment of obesity, comprising the peptide as an active ingredient.SELECTED DRAWING: Figure 1【課題】グルカゴン様ペプチド-1受容体及びグルカゴン受容体に対して天然型オキシントモジュリンよりも優れた活性を示す新規なペプチド、並びに前記ペプチドを有効成分として含む肥満予防又は治療用組成物の提供。【解決手段】GLP-1受容体及びグルカゴン受容体を活性化し得るオキシントモジュリン誘導体等、特定のアミノ酸を有するペプチド、該ペプチドをコードするポリヌクレオチド、及び該ペプチドを有効成分として含む肥満予防又は治療用の薬学的組成物。【選択図】図1