The effects of an ethanolic extract of Ferula sinaica roots on the uterine smooth muscles of rats and guinea pigs were tested in vitro using isolated uterine horns. The extract inhibited the spontaneous movements of rat and guinea pig uterine smooth muscle and also the contractions induced by oxytocin stimulation. These effects were concentration-dependent and reversible by tissue washing. These data suggest that this plant extract may have some antioxytocic potential.