A novel type of pH-responsive multifunctional mesoporous silica nanoparticle (MSN) was developed for cancerous cells drug delivery and synergistic therapy of tumor. MSNs were covered with a kind of cell-penetrating peptide, deca-lysine sequence (K10), to enhance their escape from the endosomes. After K10's primary amines were reacted with citraconic anhydride to form acid-labile β-carboxylic amides, zinc oxide (ZnO) quantum dots (QDs) were introduced to cap MSNs via electrostatic interaction. The obtained ZnO@MSN drug-delivery system (DDS) achieves "zero-premature" drug release under a physiological environment. However, once the DDS is transferred to the cancerous cells' acidic endosome, ZnO QDs would rapidly dissolve and the acid-labile amides on the side chain of K10 would hydrolyze to regenerate primary amines, resulting in the uncapping of MSNs and exposure of the cell-penetrating peptide K10. The regenerated K10 could help the DDS escape from the endosome and efficiently release the loaded drugs inside the cells. At the meantime, because of the cytotoxicity of ZnO QDs at their destination, the ZnO@MSN DDS may achieve a synergistic antitumor effect to improve the therapeutic index.