Abstract: The effect of radiotherapy can be enhanced by radiosensitizers because these compounds can improve the killing rate of radiation on tumor cells, especially on hypoxic cells. Moreover, radiosensitizers show little damage to the aerobic normal tissue and are easy to use. For these reasons, radiosensitizers are expected to become the important treatment in radiotherapy. RRx-001, a novel dinitroazetidine radiosensitizer, is an aerospace industry-derived anti-cancer agent. As an NO-donating compound, RRx-001 can pass through erythrocyte membrane, selectively bind to hemoglobin at the beta-cysteine 93 residue, and release large amounts of NO under hypoxic conditions, so as to improve radiosensitivity of hypoxic cells. RRx-001 shows good safety and tolerability in clinical studies and now is undergoing phase Ⅱ clinical trials in cholangiocarcinoma, colorectal neoplasms, ect.