Abstract: Ojbective: To observe the protective effect of matrine on radiation pneumonitis in mice.Methods: 44 mice were divided randomly into four groups: radiation alone（RT）、radiation plus matrine（MRT）、 radiation plus danshen insection、radiation plus tetramethylpyrazine.The right lungs of the mice were irradiated with 6MV-X ray,the radiation dose was 30Gy.The peritoneal cavity infusion was began 2 days before radiation for the medication groups until every observation point ended.The middle leaves of the right lungs were observed in general and studied by light-microscope after HE dyeing.Results: The radiation pneumonitis in MRT-group was lighter than the other three groups.The density of red blood cells and the density of karyotes of MRT-group were smaller than the other groups.The discrepancy was more obvious 2 moths after radiation（P＜0.01）.Conclusion: Matrine can lessen radiation pneumonitis in mice,and its protective effectiveness is better than danshen insection and tetramethylpyrazine.