Abstract: To study the differences of testicular tissue morphology and spermatogenic epithelial cells between immature（1-year-old） and sexually mature（10-year-old） Mongolian horses, the experiment collected testicular tissues of 1 year old and 10 years old Mongolian horses, and made paraffin sections and performed H.E. The tissue structure, morphology and number of spermatogenic epithelial cells were observed in the testis; subsequently, real-time fluorescence quantitative PCR and immunohistochemical staining were used to detect the differential expression of seminiferous epithelial cell-related marker genes（FGFR3, GDNF, KITLG, ITGA6, DAZL）. The results showed that there was no cavity structure in the curved fine ductus in the testicular tissue of the 1-year-old Mongolian horse. The diameter and area of the seminiferous tubules at（59.51±4.35） μm and（2 795.89±429.39） μm~2 were significantly different from those at 10-year-old（276.69±20.88） μm and（60 459.26±8 858.68） μm~2（P＜0.01）. No sperm cells were found in the tubule of the one-year-old Mongolian horse testis, and the number of spermatogenic epithelial cells（27.67±5.09） was significantly different from that of the 10-year-old（239.90±21.07）（P＜0.01）, and sperm cells appeared in the central tubule of the 10-year-old. The expression levels of spermatogonia-related marker genes（ITGA6, DAZL, FGFR3） and supporting cell-related marker genes（GDNF, KITLG） in testicular tissue of 10-year-old Mongolian horses were significantly higher than those of 1-year-old（P＜0.01）. DAZL and GDNF were expressed positively in the convoluted spermatotubule of the testicular tissue of Mongolian horses at 1 and 10 years old, and the positive expression of DAZL and GDNF at 10 years old was significantly higher than that at 1 year old. These results indicated that with the continuous development of the reproductive system and the continuous progress of spermatogenesis, there were significant differences in tissue morphology and the number of spermatogenic epithelial cells between the immature and sexually mature Mongolian horse testes.