This paper proposed a natural gelatin capped mesoporous silica nanoparticles (MSN@Gelatin) based pH-responsive delivery system for intracellular anticancer drug controlled release. In this system, the gelatin, a proteinaceous biopolymer derived from the processing of animal collagen, was grafted onto the MSN to form a capping layer via temperature-induced gelation and subsequent glutaraldehyde mediated cross-linking, resulting in gelatin coated MSN. At neutral pH, the gelatin capping layer could effectively prohibit the release of loaded drug molecules. However, the slightly acidic environment would lead to enhanced electrostatic repulsion between the gelatin and MSN, giving rise to uncapping and the subsequent controlled release of the entrapped drug. As a proof-of-concept, doxorubicin (DOX) was selected as the model anticancer drug. The loading and pH-responsive release experiments demonstrated that the system had excellent loading efficiency (47.3 mmol g(-1) SiO2), and almost no DOX was leaked at neutral. After being in the slightly acidic condition, the DOX release from the DOX-loaded MSN@Gelatin (DOX/MSN@Gelatin) occurred immediately. The cellular uptake and release studies using Hep-G2 hepatoma cells indicated that the DOX/MSN@Gelatin could be endocytosed and accumulated within lysosomes. Triggered by acidic endosomal pH, the intracellular release of the loaded DOX was obviously eventuated. Further cell viability results demonstrated that DOX/MSN@Gelatin exhibited dose-dependent toxicity and high killing efficacy (IC50 = 17.27 +/- 0.63 mu g mL(-1)), whereas the MSN@Gelatin showed negligible cytotoxicity (IC50 > 100 mu g mL(-1)). This biocompatible and effective delivery system will provide great potential for developing delivery of cancer therapeutic agents.