Abstract: The active constituents of Sanguisorba officinalis L. were extracted by ethyl alcohol， ethyl acetate, dichloromethane, nbutanol and water respectively, and the organic acids, triterpenoids and flavonoids were obtained. The antibacteria
l effects and mechanism of the extracts on Salmonella typhoon and Shigella dysenteric were studied. 
The results show that there were obvious effects of ethyl acetate, ethyl alcohol and nbutanol of S.officinalis  on S. typhoon and S.dysenteric. Compared with the control group, the difference is very significant 
(p<001). The minimum inhibitory concentration (MIC) of different bacterias were obviously different. The organic acids, triterpenoids and flavonoids in the extracts of S.officinalis  have various degree of bacteriostasis. The extracts of S.officinalis can inhibit growth of S.typhoon and S.dysenteric\% by obstructing cytoderm synthesis and cell membrane formation. The inhibition increases with the increase of t
he mass concentration of extract and the prolongation of the action time.

Key words: Sanguisorba officinalis L., extract, bacteriostasis in vitro, antibacterial mechanism, Salmonella typhoon, Shigella dysenteric