In this paper, we reported a ZnO quantum dots-based pH-responsive drug delivery platform for intracellular controlled release of drugs. Acid-decomposable, luminescent aminated ZnO quantum dots (QDs) were synthesized as nanocarriers with ultrasmall size (∼3 nm). The dicarboxyl-terminated poly(ethylene glycol) (PEG) had been introduced to NH2-ZnO QDs, which rendered it stable under physiological fluid. Moreover, a targeting ligand, hyaluronic acid (HA), was conjugated to ZnO QDs for specifically binding to the overexpressed glycoprotein CD44 by cancer cells. Doxorubicin (DOX) molecules were successfully loaded to PEG functionalized ZnO QDs via formation of metal-DOX complex and covalent interactions. The pH-sensitive ZnO QDs dissolved to Zn(2+) in acidic endosome/lysosome after uptake by cancer cells, which triggered dissociation of the metal-drug complex and a controlled DOX release. As result, a synergistic therapy was achieved due to incorporation of the antitumor effect of Zn(2+) and DOX.