Green tea extract was tested to determine its antimicrobial effects against the pathogenic bacteria Vibrio parahaemolyticus. The antimicrobial effect of green tea extract was evaluated by measuring the change in the concentration level of V. parahaemolyticus genomic DNA, which was obtained after treatment of green tea ethanol extract with neutral and acidic solvent-fractionation. Green tea extract of the neutral fraction showed concentration-dependent killing of V. parahaemolyticus, whereas green tea extract of the acidic fraction significantly inhibited the growth of V. parahaemolyticus at the minimum inhibitory concentration of 1,000~1,500 ppm.