[Objectives] In order to explore the organizational structure characteristics of reproductive organs in mammals adapting to the plateau environment, we compared the structures of male reproductive organs between Tibetan Sheep (Ovis aries) and Small-tail Han Sheep. [Methods] The testis, epididymis, and vas deferens of adult Tibetan Sheep and Small-tail Han Sheep were collected respectively. The differences in structures of reproductive organs were compared by gross anatomy, paraffin section, and conventional H.E staining. All the data were analyzed by T-test. [Results] The results indicated that the cilia in the lumen of caput epididymis and corpus epididymis were longer, on the contrary, the cilia in the lumen of cauda epididymis were shorter and displayed a clear brush border structure in Tibetan sheep (Fig. 2). There were more smooth muscle cells in the vas deferens, the lamina propria, and the mucosal layer closely adhered, and more obvious irregular folds in Tibetan Sheep (Fig. 3). The cross-sectional diameter, area, and epithelium thickness of seminiferous tubules in Tibetan Sheep were significantly lower than in Small-tail Han Sheep (P < 0.05) (Table 1); meanwhile the diameter and area of spermatogonia and primary spermatocytes, and the number of Sertoli cells were also significantly reduced in Tibetan Sheep than in Small-tail Han Sheep (P < 0.05) (Table 1). The inner diameter, outer diameter, and cilia length of the caput epididymis, corpus epididymis, cauda epididymis were significantly reduced in Tibetan Sheep (P < 0.05) (Table 2); the thickness of the columnar epithelium of the epididymis was significantly increased (P < 0.05) (Table 2), whereas the diameter of the vas deferens lumen and the thickness of smooth muscle were significantly decreased (P < 0.05) (Table 3). [Conclusion] The study suggests that the structures of reproductive organs have undergone certain adaptive changes during the long-term adaptation process of Tibetan sheep to high altitude and low oxygen environment, which may be related to the maintenance of normal reproductive performance in the plateau environment.