In order to evaluate the antimicrobial function of natural herb extracts as antimicrobial agent or packaging material for the preservation of foods and greenhouse produce, the water extract of chopi (Zanthoxylum piperitum DC.) was prepared and its antimicobial activity was determined. In the paper disk test its antimicrobial activity was increased in proportion to its concentraion. The growth of microorganisms was completely inhibited above 500ppm of its concentration. It showed wide spectrum of thermal(40 to 180oC) and pH(4 to 10) stabilities. In the electronic microscopic observation(TEM and SEM) of microbial morphological change it showed to decrease the activation of physiological enzymes and to lose the function of cell membranes. Even in the activation test of galactosidase, it seemed to weaken the osmotic function of cell membranes remarkably in comparison with chloroform and its activation corresponded to 40~50% of toluene. Zanthoxylum piperitum DC. extract seemed to be an excellent antimicrobial for the inhibition of food borne microorganisms as well as the pre servation of greenhouse produces.