Abstract: As one of the common side effects of radiotherapy for thoracic tumor, radiation induced lung injury (RILI) might develop into radiation-induced pulmonary fibrosis several months later. A lot of exploration on the mechanisms of the occurrence and development of RILI was carried out in recent years. The immunological mechanisms of regulatory T cells (Tregs) in the progress of RILI have been paid more attention by domestic and foreign scholars. The key topic of the present issue published several articles on Tregs and RILI. These articles reported the results of Tregs involved in the occurrence and development of RILI from the aspects of the changes in the number of Tregs in lung tissue and immunological mechanisms, and which provided important scientific basis for the prevention and treatment of RILI.