Introduction: The study aimed to investigate the anti-fertility effect of fennel (Foeniculim vulgare Mill) seed extract in male rats.Material and Methods: Forty Wistar rats were divided into five equal groups. The control group received distilled water and the experimental groups were orally administered 1 ml of hydro-alcoholic extract of fennel seed in four doses of 35, 70, 140, and 280 mg/kg/b.w. daily for 60 days. After the last gavage, the rats were anaesthetised and the caudal part of the right epididymis was used for sperm counting. After fixation of the testes, microscopic sections were prepared and histological changes were evaluated.Results: The number of spermatogonia after doses of 140 and 280 mg/kg and Sertoli cells after a dose of 140 mg/kg decreased significantly as compared with the control group (P < 0.05). The number of primary spermatocytes and sperm count decreased significantly in the experimental groups (70, 140, and 280 mg/kg) when compared to the control group (P < 0.05). Furthermore, thickening of the basement membrane, cell apoptosis, and irregular arrangement of the germinal epithelium were observed in the experimental groups.Conclusion: Hydro-alcoholic fennel seed extract at these doses could reduce reproductivity and has anti-fertility activity in male rats.