Bambusae Caulis in Liquamen has been used as a herbal medicine for the treatment of heat, paralysis of the hands or feet, or hemiplegia. In the present study, we investigated the effect of Bambusae Caulis in Liquamen to the phenylephrine (PE) induced contraction of isolated rat aorta Contractile force was measured with force displacement transducer under 1.5 g loading tension. Contractions evoked by PE 0.1 μM were significantly increased by low dosage of Bambusae Caulis in Liquamen, decreased by high dosage of Bambusae Caulis in Liquamen. L-NNA, ODQ and propranolol significantly altered the effect of Bambusae Caulis in Liquamen, but indomethacin did not change the relaxation of Bambusae Caulis in Liquamen. These results suggest that Bambusae Caulis in Liquamen can relax EP induced contraction of isolated rat aorta and that this decreasing contraction related to sympathetics.