To achieve the accurate diagnosis and efficient in situ therapy of malignant tumors is encouraging but still remains a big challenge. The integration of upconversion nanoparticles and mesoporous silica that can combine the diagnostic/therapeutic functions within a single platform, may provide a more advanced way for the efficient theranostics of cancer. In this study, sub-80 nm rattle-structured multifunctional Gd-UCNPs core/mesoporous silica shell nanotheranostics (UCMSNs) were successfully constructed for the co-delivery of a radio-/photo-sensitizer hematoporphyrin (HP) and a radiosensitizer/chemodrug docetaxel (Dtxl). Upon NIR excitation and X-ray irradiation, the complete tumor elimination has been achieved by the synergetic chemo-/radio-/photodynamic tri-modal therapy under the assistance of simultaneous magnetic/upconversion luminescent (MR/UCL) bimodal imaging. To the best of our knowledge, this study is the first example of achieving tri-modal synergetic therapy in one single nanotheranostic system, and we anticipate that it may serve as a particularly useful platform for the clinical diagnosis and efficient treatment of cancer from bench to beside.