Pediococcus acidilactici produces bacteriocin, which kills Listeria monocytogenes. The bactericidal mode of action of the bacteriocin against L. monocytogenes V7 was investigated by transmission electron microscopy. The bacteriocin was purified partially from the cell-free extract using Micro-Cel and cation-exchange chromatography, and the specific activity was increased 1,791 fold. The bacteriocin (6,400 AU/ ml) was inoculated with L. monocytogenes V7 and incubated for 0.5 h, 1 h, 3 h, and 6 h. The bacteriocin was found to destroy most of the cell wall and released most of the inclusions in the cells after 6 h of incubation. These results suggest that the bactericidal effect of the bacteriocin was due to bacterial lysis.