Abstract: Objective：To study the protective effect of annexin 5 (A5) on the stressinduced injuries in reproductive organ of male SD rats. Methods：Thirtytwo male SD rats were randomly divided into 4 groups, i.e., control group, sham group, surgery group and A5 group. The rats of A5 group were intraperitoneally injected with 15 μg/kg of annexin 5 per day, while the other groups were injected with equal volume of TrisHCl buffer for 21 days. The weights of testis and epididymis were measured and the amount of spermatozoon from the caudal epididymis was counted. The testis structure was observed by HE stain. The testosterone level in serum was determined by chemiluminescence assay. Results：Comparing with the control group, the coefficient of testis and epididymis, the amount of spermatozoon, and the testosterone level ［(5.10±2.61) vs (22.40±4.30) mmol/L, P<0.01］ in the surgery group were all decreased significantly. HE stain also showed that the amount of spermatids and spermatozoon reduced obviously in surgery group. Comparing with the surgery group, the amount of spermatozoon and the level of testosterone ［(19.67±2.02) vs (5.10±2.61) mmol/L, P<0.01］ in A5 group were increased significantly, and the pathologic changes of testis tissue was improved. Conclusion：Annexin5 may protect reproductive organ from injuries induced by chronic pain stress.