Abstract: Erigeroside and 3-hydroxy-4-pyranone, water-soluble constituents of Erigeron breviscapus, were synthesized and their activities investigated.The primary pharmacological studies showed that erigeroside and 3-hydroxy-4-pyranone (dose 0.86 mg/ml PRP) inhibited significantly platelet aggregation induced by ADP in vitro. The inhibiting aggregatory rates(%) of erigeroside and 3-hydroxy-4-pyranone were 32.6% and 37.6% respectively. 3-Hydroxy-4-pyranone could accelerate the blood flow of arteriolae and venulae, relieving mesenteric microcirculatory disturbances induced by noradrenaline.