Listeria spp. were isolated from a total of 402 naturally contaminated domestic ready-to-eat (RTE) vegetable samples by the conventional Food and Drug Administration protocol and confinned by API-Listeria kit. Also, the susceptibility to 12 antibiotics, polymerase chain reaction (PCR) assay for virulence gene of pathogenic Listeria monocytogenes isolates, and in vitro virulence assay using myeloma and hybridoma cells from murine and human sources were tested. Among the samples, 17 samples (4.2％) were found to be contaminated with Listeria species. Among the 17 strains of Listeria spp. isolates, only 2 strains (11.8％) of L. monocytogenes and 15 strains (88.2％) of L. innocua were identified. Antibiotic susceptibility test showed that the Listeria spp. isolates were very susceptible to the antibiotics tested, except for nalidixic acid. Among 17 strains of Listeria spp., PCR analysis showed that 2 strains of L. monocytogenes isolates proved to have a virulence hly gene, but none of L. innocua had the hly gene. Also, hybridoma Ped-2E9 cells assay showed that only L. monocytogenes isolates killed approximately 95-99％ hybridoma cells after 6 h, but L. innocua isolates had about 0-5％ lethal effect. These results indicate that PCR assay with hly primer or hybridoma Ped-2E9 cells assay could be used as a good monitoring tool or in vitro virulence test for L. monocytogenes.