Abstract: Radiation-induced brain injury (RBI) is a serious complication of patients with primary and secondary tumors in the head, neck and brain after receiving radiotherapy. Regarding the mechanism of RBI, there are several hypotheses such as vascular injury, inflammatory immune response and demyelination. Among them, inflammatory response is considered to play an important role in the pathogenesis of RBI. Microglia (MG) is the innate immune cell in the brain, which plays an important role in the pathophysiology of neuroinflammation induced by various central nervous system diseases. The author summarizes the research progress of the role of MG in RBI and its mechanism in recent years.