Background and Aim: Dexamethasone affects testis hemostasis through reduction of testosterone level . In one study dexamethasone induced spermatogenesis defects through epithelial vacuolizations and sloughing of germ cell layer. Material and Methods: Forty NMRI mice were randomly divided into four groups. Control and dexamethasone groups received normal saline and dexamethasone (5 mg/kg) respectively for 7 days. Dexamethasone and Nigella sativa(NS) (5 mg/kg) were given to the third group and the fourth group(Nigella sativa group) received 5 mg/kg Nigella sativa for 7 days. Epididymal sperm parameters were used for evaluation of the effects of dexamethasone and Nigella sativa on testis. Results: Epididymal sperm parameters) count,motility and abnormal sperm) showed significant alterations in dexamethasone group (p