Objective:To evaluate the effects of ethanol extract of leaves of Helianthus annus (H. annus) on the fecundity of Wistar rats. Methods:Forty (20 male and 20 female) Wistar rats, grouped into control, ethanol extract treated rats and untreated, were used for the study. Treated rats had 0.5 g/kg of ethanol extract orally for 2 weeks;control rats had 5%alcoholic water (solvent);and untreated rats had their normal feed and clean drinking water. Following treatment, the animals were sub-grouped into 5 mating groups to observe the coital frequency, pregnancy rate and average number of pups per group in pairs. Results:The results showed that coital frequency was unaffected by the extract treatment but pregnancy rate and number of pups per rat and per group were reduced significantly in groups II, III and IV compared to those of group I and V rats which were not treated with the ethanol extract of leaves of H. annus. Conclusions:The histo-degenerative in the gonads reportedly induced by this ethanol extract in previous studies may be responsible for the reduced fecundity observed in treated adult rats.