Radiation therapy is an effective treatment for solid tumors. Its effectiveness results from DNA damage of tumor cells induced by ionizing radiation (IR). However, IR can also destroy normal tissues surrounding tumors in treatment of cancer. Early damages are featured with acute inflammatory response. Late damages are characterized by fibrosis, which would affect the structure and function of the targeting organs, even threaten the quality of patients’ life. Previous studies suggested that radiation fibrosis process involves multiple cytokines, multiplex reactions and changes in the microenvironment. Here we review the current progress of molecular mechanisms on radiation-induced fibrosis.Cited