To provide compositions containing melittin which has high selectivity against cancer cells.SOLUTION: The present invention relates to a composition for preventing, treating, and improving cancer, which has high target properties against cancer and contains melittin nanoparticles whose half-life in blood is long.SELECTED DRAWING: Figure 13【課題】癌細胞に対する選択度の高いメリチン含有組成物を提供すること。【解決手段】本発明は、癌に対する標的性が高くて、血中半減期が長いメリチンナノ粒子を含む癌の予防、治療及び改善用組成物に関する。【選択図】図13