Abstract： Objective To study the inhibitory effects of radiotherapy and 125I seed brachytherapy on the growth of transplanted human lung cancer cell line A549 in nude mice and the impact of HIF-1αexpression after therapy.Methods Forty nude mice bearing human lung cancer cell line A549 were randomly divided into control group,radiotherapy group,125I seed brachytherapy group and radiotherapy + 125I seed group when tumor volume achieved (300±50) mm3.The tumor growth was observed and the alteration of tumor size was calculated at different time.On 15th day,the expression of HIF-1α was detected by immunohistochemistry and western blot.Results When eighth day after treatment,compared with the control group,the tumor volume of the combined treatment group was significantly smaller (t = 46.4,P ＜0.05).After fifteenth day after treatment,compared with control group,the group of radiotherapy,125I seed brachytherapy and radiotherapy + 125I seed gained the tumor control rate of 45.9 %,44.4 %,69.4 % respectively.Compared with other groups,the change of expression of HIF-1α in the combined treatment group was not significant (P ＞0.05).Conclusion Radiotherapy combined with 125I seed brachytherapy can inhibit the growth of transplanted human lung cancer cell line A549 in nude mice,and the tumor regression can be observed in early stage.But in our study,the expression of HIF-1α in tumors cannot be inhibited by 125I seed.