Stimuli-sensitive polymers, or called as smart ones, of which physical or chemical characteristics change upon pH, temperature and light, have been extensively studied in the biomedical engineering and tissue engineering field. Among them the self-assemblies from pH-sensitive amphiphilic polymer have been studied as intracellular anticancer drug carrier. With the aid of various acid-labile moieties such as acetal, orthoester, hydrazone and peptidyl linker a wide range of pH-sensitive diblock copolymer have been developed showing pH-sensitive drug release profile. However, their pH-sensitive drug release is relatively slow and passive. In this study we synthesized biodegradable poly(amino acid)-based graft copolymer with pH-sensitivity induced by charge conversion of citraconic amide bond. The physicochemical characteristics of self-assemblies were investigated with using DLS, TEM, FT-IR, and UV/Vis spectroscopy. As a model protein drug lysozyme was successfully incorporated in the core of self-assemblies and released upon a small pH drop, which are confirmed by quantification of free amine group at the graft end and lysozyme with UV/Vis spectroscopy.