Tribulus terrestris L. is an annual plant which has been commonly used in folk medicine as diuretic and against colic pains, hypertension and hypercholesterolemia in Turkey. This study investigated the effects of liophilized saponin mixture of this plant on several smooth muscle preparations in vitro. The liophilized material was obtained from dried and powdered T. terrestris L. by specific extraction method for saponins. Median lethal dose (LD50) of saponin mixture on Swiss albino mice was calculated according to Litchfield-Wilcoxon method via i.p. route. LD50 and its 95% confidence limits were 813 and 739-894 mg.kg-1 respectively. Saponin mixture has caused a significant decrease on peristaltic movements of isolated sheep ureter and rabbit jejunum preparations in a dose-dependent manner (p < 0.05). However it has been observed no effect on isolated rabbit aorta and its contractile response to KCl or noradrenaline (p > 0.05). According to these results it has been suggested that T. terrestris L. or its saponin mixture may be useful on some smooth muscle spasms or colic pains.