Abstract: Radiation pulmonary fibrosis(RPF) is a frequent side effect of thoracic radiotherapy for breast neoplasm and total body irradiation before bone marrow transplantation. Studies on its pathogenesis have arrived at molecular level. Many cytokines, adhesion molecules and vasoactive substances all play important role in the course of RPF. Moreover, there exists genetic loci that has relation with RPF. Furthermore, studies on the molecular pathogenesis of RPF have pro? vided new ideas and new measures for the precaution and therapy of RPF.