This chapter gives an overview of the radioprotective and radiosensitizing effect of curcumin. Ionizing radiations interact with biological molecules inducing radiolytic products like e(aq), *OH, *H, -OH, +H, O2, and peroxides. These free radicals damage important biomolecules and subsequently inflict deleterious effects in the organism. Whole-body exposure to ionizing radiations results in central nervous system, gastrointestinal tract, and bone marrow syndromes, whereas chronic irradiation causes cancer, birth anomalies, erythema, and dysfunctions to almost all organ of the body depending on the total dose and site of irradiation. Curcumin (diferuloyl methane), a yellow pigment present in the rhizomes of turmeric, has been used in Southeast Asia to give yellow color and flavor to curries. Turmeric has been used to treat various ailments in the Ayurvedic system of medicine in India. Recently, it has been evaluated for its radioprotective and radiosensitizing activities. Curcumin has been found to exert a dual mode of action after irradiation depending on its dose. It has been reported to protect various study systems against the deleterious effects induced by ionizing radiation and to enhance the effect of radiation. Therefore, curcumin can be very useful during radiotherapy of cancer. Administration of curcumin in patients will be able to kill the tumor cells effectively by enhancing the effect of radiation and, at the same time, protect normal cells against the harmful effects of radiation. The available information on curcumin suggests that the radioprotective effect might be mainly due to its ability to reduce oxidative stress and inhibit transcription of genes related to oxidative stress and inflammatory responses, whereas the radiosensitive activity might be due the upregulation of genes responsible for cell death.