The effect of aqueous extract of Magnifera indica (500mg/kg-body weight, orally) on the oestrous cycle, serum level of the gonadotropins and the female sex hormones, pregnancy, and body weight were investigated in adult female Sprague Dawley rats. Daily administration of extract at a dose of 500mg/kg (treated rats) and distilled water (control) were done during the 4 weeks period of determination of the length of cycle. Separate rats were used for the pregnancy study. Pregnancy was induced by allowing the female rats to mate freely at timed intervals with adult male rats. Number of implantation sites, resorption sites, viable fetuses and fetal weight were measured. Weights of rats were monitored during pregnancy. Extract treated rats had disrupted uterus cycle, with the occurrence of oestrous phase being significantly reduced(P<0.05), 1.800 +/- 0.416 days in the treated group and the control was 6.400 +/- 0.036days. Diestrous phase was significantly increased, P<0.05, treated 19.400 ± 0.653 days, control 13.100 ± 0.379 days. Serum FSH level was significantly reduced, P<0.05 in treated rats, the extract showed no significant effect on other hormones which were assayed. There was no significant effect on the number of implantation sites and viable fetuses but fetal weight was significantly reduced, P<0.05, treated 1.939 ± 0.021g, control 3.073 ± 0.031g. There was a significant reduction in weight gain of treated rats when compared with control, by weeks 3 and 4. All these results revealed that the aqueous extract of Magnifera indica may cause disruption of the oestrous cycle inhibiting ovulation, while reducing weight gain during pregnancy and reducing the fetal weight However,it has no significant effect on implantation activities. Reference 1 : 1. Olatunji-Bello I.I. and Aliu O.N (2000). Journal of Medicine and Medical Sciences 2(1): 74 – 76Reference 2 : 2. Raintree nutrition (1996). Tropical plant database for Mangifera indica. www.rainfree nutrition.com.