A therapeutic nanoparticle containing a cationic polypeptide and a polyanionic molecule, in which the cationic polypeptide, exerting antibacterial activity, forms electrostatic interaction with the polyanionic molecule, and the therapeutic nanoparticle has a diameter of less than 50 nm. Also disclosed are a pharmaceutical composition, a treatment method, and a preparation method, all related to the therapeutic nanoparticle.治療性奈米粒子包含一陽離子多肽及一多陰離子分子,其中該陽離子多肽具備抗菌活性,與該多陰離子分子形成靜電作用,且該治療性奈米粒子的直徑小於50 奈米。亦揭露與該治療性奈米粒子有關的一種醫藥組合物、治療方法及製備方法。