Abstract: The characteristic bitter taste of Vernonia amygdalina has been attributed to its anti-nutritional contents such as alkaloids, saponins, tannins and glycosides. Recently the spermiographic effect of the plant in male rats has been reported. The present study examined the effect of bitter leaf extract on 30 days oral administration of 50, 100, 200 mg kg-1 and 60 days oral administration of 200 mg kg-1 b.wt. of the extract on some fertility indices in male wistar rats. At 30 days administration, the extract produced a significant and dose dependent increase (p<0.05) in sperm concentration, percentage motility, morphology and percentage live sperm. There was a decrease in the blood level of Follicle Stimulating Hormone (FSH) but no significant increase in the levels of Leutinizing Hormone (LH) and Testosterone. Administrations of bitter leaf extract at higher dosage (200 mg kg-1 b.wt.) and duration provoked varying degrees of testicular degeneration ranging from a significant reduction in sperm concentration, motility, percentage normal morphology, percentage number of live sperm to a significant increase in the number of percentage abnormal sperm. Evidences suggest that higher dosage of bitter leaf (Vernonia amygdalina) extract administered for a longer duration could be deleterious to the testes.