Using rat thoracic aortic rings to test the relaxing effects of the 95% ethanol extract and aqueous extract of Taohong Siwu decoction (THSW) on endothelium intact or endothelium removed aortic rings. Results showed that the 95% ethanol extract (0.1, 1, 10, 100, 1000 mg•L-1) and aqueous extract (0.1, 1, 10, 100, 1000 mg•L-1) of THSW were able to relax the intact endothelium aortic rings pre-contracted by 10-6 mol•L-1 PE. 10-4 mol•L-1 L-NAME and 10-5 mol•L-1 methylene blue both were able to inhibit the relaxation other than indomethacin. For the endothelium removed aortic rings, potassium channel blocker 3×10-3mol•L-1 tetraethylammonium chloride and 10-5 mol•L-1 glibenclamide had no effect on the relaxation effects caused by the 95% ethanol extract and aqueous extract of THSW. It could be concluded that the 95% ethanol extract and aqueous extract of THSW relax blood vessel by endothelium-dependent way.