Abstract: Fish livers from different contaminant ponds of Yan-jia Lake were collected, the TCDD equivalents were measured with EROD bioassay in vitro. The comparative results of EROD bioassay in vitro to chemistry analysis and to EROD bioassay in vivo were summarized. The results from EROD bioassay in vivo and vitro had a good relationship with those from chemical analysis. The studies not only show that the CYP1A1 activity as inducer of EROD is veracious for indicating the toxicity of dioxin-like compounds in aquatic ecosystem, but also reflect that the EROD bioassay in vivo and vitro can be complementarily with each other and useful for a rapid screening of other biosamples in environment.