There are many sources of persistant organic pollutants (POPs) at southern coastal area in Korea because of many large industrial complexes and municipal cities. We monitored the genotoxicity of extracts of sediments collected from Kwangyang Bay in Korea. Sediments were collected from 13 different sampling sites and extracted with organic solvents. The concentration of PAHs, PCBs, DDTs, HCHs and CHLs in sediments were in the range of 100-9,000, 0.5-6.0, 0.1-6.0, 0.1-0.8, and 0.01-2.5 ng/g dry weight, respectively. The measurement of DNA breakage has been successfully utilized in many field studies of genotoxic effects of contaminated sediments. In vitro system was used to investigate the genotoxic potential of complex mixtures such as organic extracts of marine sediments. DNA damage was induced in blood cells isolated from flounder (Paralichthys olivaceus) by exposure to organic sediment extracts or hydrogen peroxide as positive control, respectively. The flounder blood cells exposed to hydrogen peroxide were displayed a typical tail movement. Results from experiment with flounder blood cell exposed to sediment extract showed that DNA strand breakage was positively correlated with the concentration of POPs in the sediment.