The aim of this study is to highlight the work on plant drugs and their bioactive extracts involved in male anti-fertility mechanism. The ethanol extract of Withania somnifera was found to be water soluble. In the present study we have evaluated the effective spermicidal concentration of this extract on male albino rat sperm, by conducting "Sander-Cramer test". The minimum effective spermicidal concentrations of Withania somnifera stem extract were found to be 10±0.06 mg/ million sperm. After exposure of extract, there were no morphological changes observed in the head, mid -piece & tail of sperm. In the in-vivo study, a dose dependent reduction in the epididymal sperm count and percentage motility were observed. These results showed that Withania somnifera extract has antifertility effect on male rat reproduction, sexual behavior and epdidymal sperm concentration. So ethanol extract of Withania somnifera stem is a potent spermicide which completely immobilized the one million of rat sperm within 20s.