Abstract: Objective To study the effect of different concentration of progesterone(P) on the growth and cell cycle of endometrial adenocarcinoma cell line JEC with negative progesterone receptor in vitro and its possible mechanism. Methods Two groups were set up:sample group(progesterone at different concentrations) and control group without progesterone.The proliferative capacity of endometrial adenocarcinoma cell line JEC in the culture medium with progesterone was assessed by cell counting on a haemocytomter 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 p21 in JEC was examined by FCM，and the expression of Cyclin A of JEC was examined by immunocytochemical staining and using automatic image analysis technology. Results (1)The cell counting and MTT showed that the cell numbers had significant difference in the other experimental groups compared with the control group.(2)FCM showed that progesterone(10-5mol/L) increased the cells percentage at the G0/G1 phases and decreased the cells percentage in S and G2/M phases.(3)The expression of P21 protein have no change after dealing with progesterone.(4)The expression of Cyclin A could be inhinbited obviously by progesterone. Conclusion It is suggested in the present study that progesterone inhibits the proliferation of endometrial adenocarcinoma cell line JEC in vitro which is in dose— and time— dependent manner.Its effect may be associated with the change in the expression of Cyclin A，butuncorrelated with P21 protein.