Objictive The estrogen_like activities of environmental estrogens mediated by estrogen receptor (ER) may be assayed through measuring the expressed product of the reporter gene in the recombinant yeast. Methods The recombinant yeast YM_ADER_ERE was obtained by transformation of pGAD_hER and pLacZi_2ERE, the yeast expression vector of full_length human ER cDNA and reporter vector controlled by estrogen response element (ERE) which were constructed successfully in the lab, by means of the lithium acetate method. Results The activity of ?_galactosidase, the expressed product of the reporter gene lacZ in the yeast YM_ADER_ERE, increased significantly when added in the natural estrogen 17?_estradiol (E2) compared to DMSO. In the experiment with E2 at the final concentration of 10-15 to 10-7 mol/L, the maximum effect (EAmax) and the median effect concentration (EC50) of E2 in the yeast were 94.31 U and 0.34 nmol/L respectively. Conclusion The expression of the reporter gene in the recombinant yeast was dependent on the estrogen ligand, which met with the design idea and requirement of the assay system for environmental estrogens and indicated preliminarily that the recombinant yeast estrogen system (RYES) was established successfully.