Photodynamic therapy (PDT) is a promising treatment modality for cancer management. So far, most PDT studies have focused on delivery of photo-sensitizers to tumors. O-2, another essential component of PDT, is not artificially delivered but taken from the biological milieu. However, cancer cells demand a large amount of O-2 to sustain their growth and that often leads to low O-2 levels in tumors. The PDT process may further potentiate the oxygen deficiency, and in turn, adversely affect the PDT efficiency. In the present study, a new technology called red blood cell (RBC)-facilitated PDT, or RBC-PDT, is introduced that can potentially solve the issue. As the name tells, RBC-PDT harnesses erythrocytes, an O-2 transporter, as a carrier for photosensitizers. Because photosensitizers are adjacent to a carry-on O-2 source, RBC-PDT can efficiently produce O-1(2) even under low oxygen conditions. The treatment also benefits from the long circulation of RBCs, which ensures a high intraluminal concentration of photosensitizers during PDT and hence maximizes damage to tumor blood vessels. When tested in U87MG subcutaneous tumor models, RBC-PDT shows impressive tumor suppression (76.7%) that is attributable to the codelivery of O-2 and photosensitizers. Overall, RBC-PDT is expected to find wide applications in modern oncology.