Abstract: Objective:To study the protective mechanism of Epimedium alkaloids against cyclophosphamide induced reproductive injury in male mice. Methods: First, 40 male mice of Kunming species were randomly divided into blank group and Epimedium low, medium and high dose groups to investigate whether Epimedium alkaloid had reproductive toxicity to male mice. Secondly, another 40 Kunming male mice were injected with cyclophosphamide for modeling, and randomly divided into cyclophosphamide group, cyclophosphamide-alkaloid low, medium and high dose groups. After successful modeling, the mice in each dose group were given the drug for 30 days by gavage except the cyclophosphamide group. After the last administration, mice were sacrificed and the quality of epididymis, testis and sperm of different groups of mice were measured. The contents of superoxide dismutase (SOD), malondialdehyde (MDA), testosterone and Bcl-2/Bax protein in testicular tissue were detected. Results: Epimedium alkaloid had no reproductive toxicity on male mice. Spermatozoa quality and testicular activity decreased significantly after injection of cyclophosphamide, and testicular tissue of mice was seriously damaged, which proved the success of modeling. Compared with the cyclophosphamide group, epididymal coefficient and testicular coefficient of mice in each dose group were significantly increased, sperm number increased, sperm viability increased, sperm malformation rate decreased, SOD activity in testicular tissue increased, MDA content decreased, testosterone level increased, and Bcl-2 /Bax protein ratio increased. Through the observation of testicular tissue section, the damage of testicular tissue was reduced. Conclusion: Epimedium alkaloid can protect the reproductive system of male mice to some extent.