The anti-fertility effect of the aqueous and ethanol extracts of the leaves and roots of Leonotis ocymifolia
were studied both in vivo and in vitro. The anti-implantation and anti-fertility activities of the ethanol leaves extract were 37% and 20%, respectively. The body weight recorded for 19 days starting from day 1 of pregnancy showed that all rats of the control groups showed considerable weight gains over the period of 19 days. The weight gained by the rats treated with aqueous root extract was significantly less as compared to the controls. On the contrary, those treated with both aqueous and ethanol leaf extract did not show a significant difference in their weight gains over the same period. Aqueous root and leaf extracts reduced the number of implants significantly. No significant difference was, however, observed between the average number of implants counted in rats treated with ethanol leaf extract and the control group. All extracts were observed to increase acetylcholine induced uterine contraction. The mean percentage contractions showed by these extracts in the presence of acetylcholine were significantly different from that of acetylcholine alone (P < 0.05). The results of this study suggest that the leaves and roots of this plant may possess hormonal properties that can modulate the reproductive function of the rats.