Background: Photodynamic therapy (PDT) is a promising antitumor strategy with fewer adverse effects and higher selectivity than conventional therapies. Recently, a series of reports have suggested that PDT induced by Cerenkov radiation (CR) (CR-PDT) has deeper tissue penetration than traditional PDT; however, the strategy of coupling radionuclides with photosensitizers may cause severe side effects. Methods: We designed tumor-targeting nanoparticles (I-131-EM@ALA) by loading 5-aminolevulinic acid (ALA) into an I-131-labeled exosome mimetic (EM) to achieve combined antitumor therapy. In addition to playing a radiotherapeutic role, I-131 served as an internal light source for the Cerenkov radiation (CR). Results: The drug-loaded nanoparticles effectively targeted tumors as confirmed by confocal imaging, flow cytometry, and small animal fluorescence imaging. In vitro and in vivo experiments demonstrated that I-131-EM@ALA produced a promising antitumor effect through the synergy of radiotherapy and CR-PDT. The nanoparticles killed tumor cells by inducing DNA damage and activating the lysosome-mitochondrial pathways. No obvious abnormalities in the hematology analyses, blood biochemistry, or histological examinations were observed during the treatment. Conclusions: We successfully engineered a nanocarrier coloaded with the radionuclide I-131 and a photosensitizer precursor for combined radiotherapy and PDT for the treatment of breast cancer. [GRAPHICS] .