Abstract: Objective:To assay the regulation effects of estrogen and tamoxifen on urokinase-type plasminogen activator （uPA） and its receptor （uPAR） gene expression.Methods:The SGC-7901 gastric cancer cell line was treated with estradiol （E2） and tamoxifen. Dot blots of total RNAs were hybridized with appropriate cDNA probes measurement of the mRNA level for uPA and uPAR in treated SGC-7901.Results:After treatment with E2 （0.1 μmol/L） alone, SGC-7901 cells uPA and uPAR mRNA expression levels increased about 2.9-or 2.1-fold respectively. When SGC-7901 cells were treated with E2 in the presence of tamoxifen （0.01 g/L）, uPA and uPAR mRNA expression were inhibited. Tamoxifen inhibited about 43.4% of the uPA mRNA induced by E2, whereas uPAR mRNA was inhibited by about 53.4% in the same experiment.Conclusion:These results suggest that uPA and uPAR gene expression may be regulated by estrogen in gastric cancer cells. The effects of estrogen on up-regulation of uPA and uPAR mRNA expression may be inhibited in part by tamoxifen.