Abstract: Objective To study the effect of different concentration of estrogen(E₂) on the growth of estrogen receptor negative of endometrial adenocarcinoma cell line JEC in vitro. Methods Endometrial adenocarcinoma cell line JEC originated from human endometrial adenocarcinoma was cultured in vitro. Two groups were set up: sample group (17-β estradiol at different concentrations) and control group without estrogen. The proliferative capacity of endometrial adenocarcinoma cell line JEC in the culture medium with 17-β estradiol was assessed by cell counting on a haemocytometer and evaluated by the means of 3-(4,5-dimethylthiazol-z-yl)-2,5-dipheny tertrazolium blue (MTT)and cell cycle was analyzed by flow cytometry (FCM). The expression of cyclin A of JEC was examined by immunocytochemical staining and using automatic image analysis technology. Results （1）The cell numbers in the fourth day after dealing with 1×10^-7 and 1×10^-6 mol/L concentrations of E₂ were more than that in control group. The optical density of JEC cell in the 72th hour after dealing with 1×10^-6 mol/L concentration of E₂ was higher than that in control group（P<0.01）. There was no statistics significant difference in the other experimental groups compared with the control group(P>0.05).（2）FCM showed that 17-β E₂(1×10^-6mol/L) increased the cells percentage at the S and G₂/M phases of cell cycle and decreased the cells percentage in G₀/G₁ phases of cell cycle.（3）Analysis on expression of intracellular cyclin A protein showed that estradiol could obviously up-regulate cyclin A protein by the immunohistochemical method of SABC. Conclusion It is suggested in the present study that estrogen can stimulate the proliferation of endometrial adenocarcinoma cell line JEC in vitro.There is an accordant dose-response and time-response relationship. In addition, its effect may be associated with the change in the expression of cyclin A.