The antifertility activity of methanol extract of Cuscuta reflexa Roxb. stem (MECR) and Corchorusolitorius Linn. seed (MECO) were studied on male Swiss albino mice. The extracts were found todecrease sperm count, percentage of motile sperm and testosterone level in treated mice whencompared with vehicle control after 17 days of treatment. The weight of gonads, epididymis weredecreased whereas no significant changes of the body weight of mice were observed aftermethanol extract treatments. The fertility test showed 100% negative result in MECR and MECOtreated mice at medium and high dose level of treatment. MECR and MECO in low (25 mg/kgand 15 mg/kg, respectively), medium (50 mg/kg and 20 mg/kg, respectively) and high (75 mg/kg and 25 mg/kg, respectively) dose level caused a simultaneous fall in testicular Δ5-3β–hydroxysteroid dehydrogenase and glucose-6-phosphate dehydrogenase activities which are involved intesticular steroidogenesis. Total cholesterol and ascorbic acid content in testis were increasedsignificantly in gonads. The activities of lactate dehydrogenase, malic dehydrogenase and ascorbic acidoxidase were reduced whereas that of carbonic anhydrase was increased significantly in the testisof MECR and MECO treated mice. All these observations indicate that the methanol extract of C.reflexa stem and C. olitorius seed produced antifertility activity in sexually matured male mice,which may be due to inhibition of gonadal steroidogenesis. This activity may be attributed due tothe presence of flavonoids and steroids, respectively.