Aim To observe the effect of testosterone undecanoate(TU) on intima restoration of iliac artery after injury in male rabbit.Methods Twenty-five male Japanese rabbits were randomized into 5 groups(5 in each):control group,castrated group,small dose group(3 mg/kg),middle dose group(6 mg/kg) and large dose group(12 mg/kg).All five groups of rabbits were castrated except the control group.At the fourteenth day after castration all animals were performed with endothelium denudation at the right iliac artery.At the seventh,fourteenth and twenty-first day after castration,the last three groups of rabbits were intramuscularly injected with testosterone undecanoate,whereas control group and castrated group were intramuscularly injected with 0.9% saline.Blood sample were collected for determination of total testosterone(TT) at different time.At the twenty-eighth day after castration,all animals were killed by air embolism.The endothelial structure and morphological changes were observed with scanning electron microscope and HE staining.Results The hyperplasia of endometrium was serious in castrated group,small dose group and middle dose group at the sight of light microscope,whereas in large dose group this hyperplasia is as light as that in control group.The intima-to-media ratio of iliac artery in castrated group,small dose group and middle dose group(respectively 1.25±0.10,0.90±0.10,and 0.74±0.11) were obviously larger than those in control group(0.22±0.05)(p<0.01),whereas no significant difference was found between large dose group(0.26±0.07) and control group(p>0.05).Scanning electron microscopy showed that the endothelium of control group was smooth and continuous,and the cells were in good order.Whereas in castrated group almost no endothelial cell was observed.There were a few isolated areas having endothelial cells in small dose and middle dose groups.In large dose group,the arrangement of endothelial cells got close to normal state and have small deletion occasionally.At the twenty-eighth day after castration,serum level of total testosterone(TT) in large dose group was similar to that before castration and in control group.Serum level of TT in other groups was obviously lower than that in control group.Conclusion Testosterone,at physiological level,can protect vascular endothelium and inhibit intima hyperplasia in male rabbit.