Abstract: Radiation pneumonitis and pulmonary fibrosis are important dose-limiting side effects of radiotherapy that influence the prognosis and quality of life of patients with thoracic cancer. The disorder of the immune system plays a key role, especially macrophages. With the discovery of underlying molecular mechanisms, including the chemotaxis and polarization of macrophages, the infiltration of inflammatory cells, the release of inflammatory and pro-fibrotic factors, extracellular matrix deposition and the remodeling of lung structure, increasing strategies are under investigation to facilitate the prevention or treatment of lung injury via targeting macrophages. In this paper, the role of macrophages in the development of radiation pneumonitis, pulmonary fibrosis, and potential drug use strategies were reviewed.