In this work, pH-responsive polypeptide-based nanogels are reported as potential drug delivery systems. By the formation of pH-sensitive benzoic imine bonds, pH-responsive nanogels are constructed using hydrophilic methoxy poly(ethylene glycol)-b-poly[N-[N-(2-aminoethyl)-2-aminoethyl]-l-glutamate] (MPEG-b-PNLG) and hydrophobic terephthalaldehyde (TPA) as a cross-linker. At pH 7.4, MPEG-b-PNLG nanogels exhibit high stabilities with hydrophobic inner cores, which allow encapsulation of hydrophobic therapeutic agents. Under tumoral acidic environments (pH ～6.4), the cleavage of benzoic imine bonds induces the destruction of MPEG-b-PNLG nanogels and leads to rapid release of their payloads. The formation and pH sensitivity of the nanogels are investigated by dynamic light scattering. These nanogels exhibit excellent stabilities in the presence of salt or against dilution. The globular morphologies of the nanogels are confirmed using transmission electron microscopy. Doxorubicin is used as a model drug to evaluate drug encapsulation and release. Finally, the anticancer activities of the drug-encapsulated nanogels are assessed in vitro.