The present disclosure relates to a method of treating cancer using a composition including a target-specific self-illuminative nanocomplex which includes a self-illuminative nanocomplex including a quantum dot and a modified self-illuminative protein (m-Rluc8), a targeted cancer-specific molecule and a hydrophilic polymer, and a method of preparing the composition. Since the high efficiency self-illuminative nanocomplex may have high target specificity by chemically binding to a target-specific molecule, it can be effectively used in cancer treatment using a nanometer-scale laser light source, and therefore it is expected to propose a new paradigm of nanoptic therapeutics.