Luk (Laccifer lacca Kerr) is an animal origin drug with possible contraceptive properties. Objective: Antiovulatory activity was performed on mature female Wistar rats by cyclic administration of Luk (Lac). The animals were divided into 4 groups of six each, one control group and three test groups (A, B and C). Control group received 1 ml 0.5% carboxy methyl cellulose. Test groups A and B were treated with Luk maghsool with water (LMW) in the dose of 470 mg/kg and 800 mg/kg, respectively. Test group C was treated with 800 mg/kg Luk maghsool with Izkhar Rewand (LMIR), and vaginal smear and histological and biochemical studies were performed for 15 days. The results displayed a remarkable increase in the duration of estrus cycle and diestrus phase. In test groups treated with LMIR, a decrease in estrus and proestrus phase was observed. An increase in uterine weight was observed in treated groups. Estrogenic nature of the test drug was assessed by noting the times taken for vagina to completely open after 7 days of treatment in immature rats. For this the animals were dividing into four groups i.e. Plain Control receiving CMC (0.5%), Test Group A and B receiving LMW (800 mg/kg) and LMIR (800 mg/kg) respectively where as standard group was given Ethinyl estradiol (0.02mg/kg). A significant Luk mediated estrogenic activity was exhibited by immature vaginal opening when compared to control, suggesting Lac as an antifertility agent due to its estrogenic nature. The findings of the present study may suggest Luk as effective antifertility agent devoid of side effects associated with other contraceptive pills.