As heavy-metal-based nanoscale metal-organic frameworks (nMOFs) are excellent radiosensitizers for radiotherapy via enhanced energy deposition and reactive oxygen species (ROS) generation, we hypothesize that nMOFs with covalently conjugated and X-ray triggerable prodrugs can harness the ROS for on-demand release of chemotherapeutics for chemoradiotherapy. Herein, we report the design of a novel nMOF, Hf-TP-SN, with an X-ray-triggerable 7-ethyl-10-hydroxycamptothecin (SN38) prodrug for synergistic radiotherapy and chemotherapy. Upon X-ray irradiation, electron-dense Hf12 secondary building units serve as radiosensitizers to enhance hydroxyl radical generation for the triggered release of SN38 via hydroxylation of the 3,5-dimethoxylbenzyl carbonate followed by 1,4-elimination, leading to 5-fold higher release of SN38 from Hf-TP-SN than its molecular counterpart. As a result, Hf-TP-SN plus radiation induces significant cytotoxicity to cancer cells and efficiently inhibits tumor growth in colon and breast cancer mouse models.