Abstract: The B.sutilis, E.coli and S.aureus were used as indicator-bacteria to study the mode of action of the extract of Eleocharis tuberosa peel (EETP) to prevent the growth of bacteria by mears of growth curve method and recultivating agarblock. The results showed: low concentration (0.1%～0.2%) of EETP could prevent the growth of bacteria while a higher concentration (0.4%) could kill the bacteria to certain degree. The observation under the microscope, phase showed that in the culture solution of bacteria with EETP, the bacteria density lowered obviously and their shapes also showed obvious changes.

Key words: extract of eleocharis tuberosa peel (EETP), antibacterial action, mode of action