Objective:To investigate the radiation damage on rabbit trachea by 125I brachytherapy seeds implantation using factorial design,and evaluate the security of clinical application. Methods:The 2×2 factorial design was applied to observe the effects of I-125 brachytherapy seeds and radiation time,and the interaction of the two factors.16 healthy male New Zealand rabbits weighing 2.5～3.0 kg were divided into 8 pairs by heterogeneous paired rules. Two groups(14 d,30 d)were made further randomly,each group had 4 pairs. Two rabbits in the each pair were distributed into two groups:test group(0.5 mCi×3)and control group(non-radioactive seeds×3). Three seeds implaned in the trachea wall had a linear distribution at intervals of 10 mm. On the 14th day and the 30th day after operation,the tracheas of the corresponding group were collected and examined by visual observation,histopathologic examination by HE stain,and transmission electron microscopy to understand the degree of inflammatory injury. All the statistical analysis were performed by STATA 7.0 software. Results:Perforation and thrombogenesis were not observed in both test group and control group on the 14th day and the 30th day. There was no statistical difference of the inflammation score in the test group, compared with the control group(P > 0.05). Injuries of radiosensitive cellular organelle were observed by transmission electron microscopy in the test group,but there was no significant difference of the electron microscopic examination between the 14th day and the 30th day. Conclusion:Implantation of three 0.5 mCi I-125 brachytherapy seeds at intervals of 10 mm has little radiation damage of the rabbit trachea and is safe for clinical application.