The use of medicinal plants in human and animal health care systems is well documented in ancient literature. However, excessive consumption of these plants could cause damage to some body tissues as well as impair their functions. There is dearth of information on the medicinal use of Costus lucanusianus in males hence this study was designed to investigate the effect of methanolic leaf extract of C. lucanusianus (MLECL) on male reproductive parameters using albino rats as model. Twenty animals were divided into four groups. Group A (Control) received 0.5ml/kg of 20% Tween 80 (vehicle), Group B (100 mg/kg of MLECL), Group C (200 mg/kg of MLECL), Group D (300 mg/kg of MLECL) by oral gavage daily for 28 days. Thereafter, Animals were anaesthetized and testes collected, homogenized and used for determination of sperm characteristics. Blood was collected for hormonal assay (testosterone) using ELISA. Histopathological study of the testes and epididymides were conducted. Methanolic leaf extract of C. lucanusianus has no significant (p>0.05) effect on sperm cell count and characteristics relative to the control, although the percentage of the sluggishly motile sperm cells increased in a dose dependent manner. No abnormality was observed in the testicular and epididymal sections of rats in the treated groups except the thickened interstitial spaces of testicular sections of rats treated with 200 and 300 mg/kg MLECL. It is therefore concluded that Costus lucanusianus methanolic leaf extracts have no deleterious effect on male reproductive parameters and can be considered relatively safe in male fertility