A natural polysaccharide-based nanogel has been synthesized and characterized as pH-sensitive drug delivery system for poorly water-soluble anticancer drugs. In this work, methacrylated hyaluronic acid (MAHA) was used to prepared acid degradable nanogels by a surfactant-free polymerization method in water, where 2,2-dimethacroyloxy-1-ethoxypropane (DMAEP) served as a pH labile cross-linker. Nanogels of different cross-linking density were prepared and doxorubicin (DOX) was successfully encapsulated into the nanogels with drug-loading contents (DLC) ranging from 7.67 to 12.15%. An accelerated DOX release was found in acidic conditions. Cytotoxicity study showed that the DOX loaded nanogels have significantly enhanced cytotoxicity in vitro compared with the nonsensitive ones. Confocal microscopy revealed that there was more DOX in the nuclei of tumor cells when incubated with DOX-loaded pH sensitive nanogels for 3 to 12 h. The enhanced anticancer activity of DOX-loaded pH-sensitive nanogels was also verified by in vivo therapeutic study on mice, in which tumor volume evolution was measured and tumor tissues cell apoptosis and proliferation was examined.