Aim: To investigate the effect of androgen on the structure of corpus cavernosum. Methods: Thirty mature rats were randomized into 3 groups, i.e., simple castration, castration with testosterone (T) supplementation and sham-operated controls. One week after operation, the animals were sacrificed and corpora cavenosa harvested. Apoptosis was detected with the in situ end labeling (ISEL) techniques and DNA fragment analysis. Results: The apoptotic rate was 4.19% in the simple castrated rats, 0.2% in castrated rats supplemented with T and 0.14% in the controls. Significant difference was found between the simple castrates and other two groups (P<0.01). When comparing the T-supplementation group with the controls, there was no statistical difference (P>0.05). Conclusion: Castration induced apoptosis in rat corpus cavernosum, that could be prevented by T supplementation. It suggests that androgen plays an important role in maintaining the structure of corpus cavernosum.