Radiosensitizers assist radiotherapy in providing greater tumor inactivation. Currently there is a search for natural radiosensitizer components which are expected to provide lesser side effects than chemical radiosensitizers. Eucheuma cottonii is a plant with antioxidant and anti-tumor effects. This review aims to search for the potential use of Eucheuma cottonii as a radiosensitizer. This is a mixed review study, where the main component is a systematic review and then followed by a narrative review. This review suggests that Eucheuma cottonii has the potential to become a radiosensitizer, by interfering with the cell cycle control mechanisms and reactivation of p53. Further research is needed to explore the synergistic effect of the combined use of radiotherapy and Eucheuma cottonii. © 2021 Putri et al.