The purpose of this work was to investigate the physiological characteristics of Lactobacillus sp. JK-8 isolated from a shrimp aquaculture pond. The strain JK-8 was grown on MRS media, and morphological and physiological characteristics of the strain were examined. The bacterium was identified as a strain of the genus Lactobacillus on the basis of BIOLOG test. Strain JK-8 produced both lactic acid and acetic acid, which were responsible for the pH decrease during growth. Concentrations of lactic acid and acetic acid increased to 192.8 mM and 43.6 mM, respectively, and the initial pH 7.0 of the cultures decreased to 3.8 at the end of incubaction. The bacteriocidal effect against eight target bacteria was examined with 5-fold concentrated culture supernatants. All bacteria tested in this work were completely killed within 3 hrs after treatment with the culture supernatant. The bacteriocidal effects were clearly observed, only when the pH of the culture supernatants were not adjusted. HPLC was used to reslove lactic acid and acetic acid in the culture solution, and GC-MS was used to verify the metabolites.