In this study, we utilized X-ray-induced photodynamic therapy (X-PDT) against triple-negative breast cancer (TNBC) cells. To achieve this, we developed a liposome delivery system that co-loaded protoporphyrin IX (PPIX) and perfluorooctyl bromide (PFOB) in a rational manner. Low-dose X-ray at 2 Gy was employed to activate PPIX for the generation of reactive oxygen species (ROS), and the co-loading of PFOB provided additional oxygen to enhance ROS production. The resulting highly toxic ROS effectively induced cell death in TNBC. In vitro X-PDT effects, including intracellular ROS generation, cell viability, and apoptosis/necrosis assays in TNBC cells, were thoroughly investigated. Our results indicate that the nanocarriers effectively induced X-PDT effects with very low-dose radiation, making it feasible to damage cancer cells. This suggests the potential for the effective utilization of X-PDT in treating hypoxic cancers, including TNBC, with only a fraction of conventional radiotherapy.