Abstract: Dynamic change was studied in EROD activity in the liver and sex hormone in the blood serum of Carassius auratus.After exposure to different concentrations of polychlorinated biphenyls(PCBs),and the correlation between them was also discussed.Results show that EROD in the liver of Carassius auratus was induced and increased in activity with the increasing of PCBs concentration,demonstrating that the former is positively related to the latter.The activity of EROD also rose with the time,reaching dynamic balance after 10 days.Compared with CK,the content of testosterone in the blood serum of the fish rose with the concentration of PCBs,but declined with the exposure time,while the content of estradiol therein rose significantly with both the concentration and the time,indicating that PCBs have certain environmental estrogen effect on(fishes).The results also indicate that within a certain range of concentrations,EROD activity was negatively related to testosterone content,but positively related to estradiol content in blood serum of the fish.Concurrent changes in EROD in the liver and sex hormone in the blood serum of fish could be cited as the bio-indicator to evaluate ecological effect of initial PCBs pollution.