Bitter Melon (Momordica charantia) is a plant known widely particularly in the Indo-Malayan region for its uses in various ailments as reported in literature. However, little is known for its effect on the female reproductive system. The aim of this project was to evaluate the effect of oral administration of methanolic seed extract of Momordica charantia on the estrous cycle and the histology of the ovary and uterus in Sprague-Dawley (S-D) rats. A total of 20 adult cyclic female S-D rats (4-day cycles), weighing between 110‒ 140 g were used. These were divided into 4 groups (A, B, C and D) of 5 rats/ group. The dose of the extract administered was 25 mg/100g body weight and the route of administration was oral by gastric gavages with a metal canula. Groups A and B were both treated with a daily dose of the extract for 28 days (7cycles) and vaginal smear monitored within this period between 9.00‒ 10.00 am daily. Animals in Groups C and D (control) were fed distilled water and vaginal smear monitored daily throughout the duration of the experiment. The effect of withdrawal of the extract was studied in Group B which was treated with distilled water for another 28 days. The rats were sacrificed by cerebral dislocation. Groups A and C at the end of the first 28 days while Groups B and D at the end of the second 28 days. The ovaries and uterii were harvested for histological studies. Irregular changes in the phases of the estrous cycle in all the treated rats were observed. The diestrous phase was increased while the proestrous and estrous phases were decreased significantly. These effects were reversible on withdrawal of the extract. Histological sections did not show any difference between the ovarian and uterine tissues of the treated and control respectively. The extract resulted in a reversible variation in the estrous cycle pattern. Histological sections reviewed were essentially normal.