The purpose of this work was to investigate the antibacterial activity of Lactobacillus plantarum YK-9 isolated from fermented Kimchi. Morphological and biochemical characteristics of L. plantarum YK-9 were examined. Phylogenetic analysis using 16S rRNA sequencing was performed to identify the strain, and the strain could be assigned to Lactobacillus plantarum, designated as L. plantarum YK-9. The strain was registered in GenBank as [FJ669130]. During the incubation period of L. plantarum YK-9, the changes of bacterial growth and residual organic acids were monitored. HPLC was used to confirm the organic acids produced in the cultures as metabolites. L. plantarum YK-9 produced both lactic acid and acetic acid, which were responsible for the pH decrease during growth. Initial pH 7.0 of the cultures decreased to 3.6 at the incubation after 72 hours, and concentrations of lactic acid and acetic acid increased to approximately 588.7 mM and 255.5 mM, respectively. The antibacterial activities against food-poisoning causing bacteria were examined with 20-fold concentrated culture supernatants from L. plantarum YK-9, and the antibacterial effects were clearly observed against all the bacteria tested in this work.