We have developed a novel type of polymer nanogel loaded with anticancer drug based on bio-derived poly(γ- glutamic acid) (γ-PGA). γ-PGA is a highly anionic polymer that is synthesized naturally by microbial species, most prominently in various bacilli, and has been shown to have excellent biocompatibility. Thiolated γ-PGA was synthesized by covalent coupling between the carboxyl groups of γ-PGA and the primary amine group of cysteamine. Doxorubicin (Dox)-loaded γ-PGA nanogels were fabricated using the following steps: (1) an ionic nanocomplex was formed between thiolated γ-PGA as the negative charge component, and Dox as the positive charge component; (2) addition of poly(ethylene glycol) (PEG) induced hydrogen-bond interactions between thiol groups of thiolated γ-PGA and hydroxyl groups of PEG, resulting in the nanocomplex; and (3) disulfide crosslinked γ-PGA nanogels were fabricated by ultrasonication. The average size and surface charge of Dox-loaded disulfide cross-linked γ-PGA nanogels in aqueous solution were 136.3 ± 37.6 nm and -32.5 ± 5.3 mV, respectively. The loading amount of Dox was approximately 38.7 ?g per mg of γ-PGA nanogel. The Dox-loaded disulfide cross-linked γ-PGA nanogels showed controlled drug release behavior in the presence of reducing agents, glutathione (GSH) (1- 10 mM). Through fluorescence microscopy and FACS, the cellular uptake of γ-PGA nanogels into breast cancer cells (MCF-7) was analyzed. The cytotoxic effect was evaluated using the MTT assay and was determined to be dependent on both the concentration and treatment time of γ-PGA nanogels. The bio-derived γ-PGA nanogels are expected to be a well-designed delivery carrier for controlled drug delivery applications.