We have developed a novel type of polymer nanogel loaded with anticancer drug based on bio-derived poly(${gamma}$-glutamic acid) (${gamma}$-PGA). ${gamma}$-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 ${gamma}$-PGA was synthesized by covalent coupling between the carboxyl groups of ${gamma}$-PGA and the primary amine group of cysteamine. Doxorubicin (Dox)-loaded ${gamma}$-PGA nanogels were fabricated using the following steps: (1) an ionic nanocomplex was formed between thiolated ${gamma}$-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 ${gamma}$-PGA and hydroxyl groups of PEG, resulting in the nanocomplex; and (3) disulfide crosslinked ${gamma}$-PGA nanogels were fabricated by ultrasonication. The average size and surface charge of Dox-loaded disulfide cross-linked ${gamma}$-PGA nanogels in aqueous solution were $136.3{pm}37.6$ nm and $-32.5{pm}5.3$ mV, respectively. The loading amount of Dox was approximately 38.7 ${mu}g$ per mg of ${gamma}$-PGA nanogel. The Dox-loaded disulfide cross-linked ${gamma}$-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 ${gamma}$-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 ${gamma}$-PGA nanogels. The bio-derived ${gamma}$-PGA nanogels are expected to be a well-designed delivery carrier for controlled drug delivery applications.