Abstract: AIM To study the effects of praeruptorin C (pra-C) on conscious renovascular hypertensive and normotensive rats and the vascular resistance of vertebral, left circumflex coronary and femoral artery in anesthetized dogs. METHODS Hypertensive rats were obtained after the left renal arteries of normal rats were narrowed to 0.2 mm diameter by silver clips. Systotic blood pressure was measured by the tail cuff method. Measurements of systolic blood pressure were carried out before administration of the drug as well as 2, 4, 6, 20 and 24 h after drug administration. Hypertensive and normotensive rats were given pra-C 20 mg·kg^-1 orally once daily for 30 days. Using sum of squares of deviations from the mean data were analysed and compared with the controls before and after drug administration. Nifedipine was compared with pra-C on the same dose. Vascular resistance were measured on the constant rate perfusion preparation. RESULTS Pra-C reduced significantly the blood pressure in hypertensive and normotensive rats. The peak effect of pra-C and nifedipine were observed 4-6 h and 2-4 h after drug administration respectively. The hypotensive effect of pra-C was similar to that of the nifedipine at the same dose, but the action of oral pra-C lasted longer than that of nifedipine. The blood pressure lowering effect of pra-C after 3 weeks (20-30 d) of treatment is even more potent than at the beginning (1-15 d) of the trial. This indicates that there is no acquired tolerance in blood pressure. Pra-C 20 μg·kg^-1 or 100 μg·kg^-1 iv in dogs produced distinct fall of vascular resistance in vertebral, left circumflex coronary and femoral arterial resistance. Peak of effect was observed 50-60 min after drug administration. Reduction in vertebral vascular resistance was much more than that of the other two arteries. However, the effects recovered to its initial values 70 min after medication. The medication caused a reduction of systolic blood presure and slowing of heart rate. Pra-C is better than nifedipine in slowing heart rate. Pra-C prolonged the tolerance to anoxia in mice. CONCLUSION These results suggest that the antihypertensive action of pra-C may be due to peripheral vasodilation. It is reasonable to anticipate that pra-C may be an agent of choice in the treatment of hypertensive encephalopathy.