We have examined the relaxational response to the water extract of Angelica gigas $N_{AKAI}$ (AG), Gingko biloba $L_{INNE}$ (GB), Acanthopanax senticosus $H_{ARMS}.$ (AP) and Augumented-Four-Substance Decoction (AG-FSD, GB-FSD, AP-FSD) in isolated thoracic aorta from sprague dawley(SD) rat. Rat thoracic aorta was investigated in vessel segments suspended for isometric tension recording by polygraph. Responses to AG, GB, AP and AG-FSD, GB-FSD, AP-FSD were investigated in vessels precontracted with 5-hydroxytryptamine(5-HT) were compared in vasodilation effect. We found that the thoracic aorta segments responded to AG, GB, AP and AG-FSD, GB-FSD, AP-FSD with a dose-dependent vasodilation. The 5-hydroxytryptamine induced contraction at $10^{-4}M$ were inhibited by 26.3%, 75.8%, 87.5% and 6.9%, 22.6%, 30.8% after addition of the 0.1 g/mL water extract of AG, GB, AP and AG-FSD, GB-FSD, AP-FSD. In conclusion, AG, GB, AP and AG-FSD, GB-FSD, AP-FSD induced relaxation in the isolated rat thoracic aorta were composed of dose-dependent relaxation. AP-FSD has very potent vasodilation.