This study investigated the effects of baicalin on activity and gene of CYP1A in liver of flounder, .50 mg/kg·d, 100 mg/kg·d (middle dose group) and 200 mg/kg·d (high dose group). Group fed with saline was set as control. EROD(the marker enzyme of CYP1A) activity and gene of each group were measured on day 3, day 6 and day 9. Results on enzyme activity showed that the three experimental groups had no obvious change on EROD activity after 3 days compared with contuol group (<0.05). On day 6, high does group had extremely significant increase (P<0.05) in EROD activity compared with contuol group. On day 9, EROD activities of high dose group and middle dose group both extremely significantly increased (<0.05). Results of semi-quantitative RT-PCR showed that CYP1A expression of all experimental groups was up-regulated, and the extent of up-regulation was positively correlated the baicalin, which was identical with the result of CYP1A activity. It was indicated that the baicalin as an inducer could stimulate the CYP1A expression to increase the protein transcription and the