PROBLEM TO BE SOLVED: To provide a novel technique suitable for the production of a composite particle containing an anionic polymer and a peptide.SOLUTION: An anionic polymer and a peptide are mixed in an aqueous solvent with a pH of 5 or less.SELECTED DRAWING: None【課題】アニオン性ポリマーとペプチドを含む複合粒子の製造に好適な新規の技術を提供する。【解決手段】pHが5以下の水系溶媒中でアニオン性ポリマーとペプチドとを混合する。【選択図】なし